(Thor I#216 (fb) / Official Handbook of the Marvel Universe#7: Mercurio entry) - Over a period of months, Mercurio used Sarron's wealth to find the necessary materials to build the energy transformer that would steal Earth's electromagnetic field.

(Thor I#204 (fb) - BTS) - Mercurio, as Karl Sarron, bought the building at which Dr. Donald Blake practiced.

(Thor I#216 (fb) / Official Handbook of the Marvel Universe#7: Mercurio entry) - In the course of his mission, Mercurio detected unusual energy emanations coming from the office rented by Blake. He soon learned that energy came from Blake's transformation into Thor.

(Thor I#204 (fb) - BTS) - In Donald Blake's absence Sarron had Blake's office closed.

(Thor I#208 (fb) - BTS) - Mercurio accumulated energy residue left behind by Blake's transformations into Thor from inside Blake's office. He hoped to gain enough power to return him to his natural form, from which he could then transfer Earth's electromagnetic field to Gramos, restoring its polarity.

(Thor I#204) - When Blake returned to Earth from a lengthy adventure in outer space as Thor, he was surprised that his office was closed. Sarron introduced himself to Blake as the building's new owner, and told Blake that he would have to prove his former arrangements and payments to Sarron before Blake's office would be opened again. Sarron expected to see Blake in his office the following Monday.

(Thor I#208) - After receiving a potent charge from Blake's office into his Dimensional Oscillator, Mercurio contacted the leader of Gramos, who reiterated the urgency of his mission. Mercurio used the oscillator to restore his true form, but found it only possessed the charge to do so halfway, leaving only his left half his normal dark-blue, with his right half now red. Realizing he needed more power directly from Thor to complete the transformation, he waited for Thor to return and then attacked him. Mercurio continued to accumulate power as they fought, and Thor found all of his power ineffective against him. When the Warriors Three arrived to help Thor, he fled, returning after reviewing some literature as Don Blake. A plan in mind, Thor hurled a steel girder at Mercurio, who melted it, but was then coated in molten metal. The iron covering contained the forces within Mercurio so thoroughly that his powers overloaded, and Mercurio was seemingly consumed in the process.

(Thor I#214 (fb)) - Mercurio seemed to die, but was instead summoned to another level of space, where he found himself drawn into a mystic whirlpool that drew him to Xorr the God-Jewel. Detecting Mercurio's approach, Xorr determined that "in this plane of existence, he cannot harm us, and he may pass." Mercurio heard this "ghost-voice" as he struck the surface of the vast crimson jewel, and something happened within his mind and body

(Official Handbook of the Marvel Universe#7: Mercurio entry) - Mercurio's rescue having been an accident, Xorr returned him to Gramos.

(Thor I#214 (fb)) - When his mind stopped reeling from that transformation, Mercurio found himself returned to Gramos and in the presence of the Great One himself.

(Thor I#216 (fb)) - Mercurio's leader reaffirmed the importance of his mission, sending him into the Dark Nebula to claim the power of the God-Jewel to save their world.

(Thor I#214) - (Presumably led by Mercurio), the Gramosians to assault the Miners of the Dark Nebula (Kagg, Quellor, Rothgar) in order to gain the substance of Xorr. The miners knew them only as raiders, and they considered themselves fortunate to be able to repel the raiders before they reached the mine.

(Thor I#214) - Mercurio led a force of Gramosians to assault the mines  However, the Miners were assisted by a force of Asgardians who had been traveling through that region of space, including Fafnir, Heimdall, Hildegarde, Hogun, Odin, and Thor. As Thor fought Mercurio, the other Asgardians fought the Gramosians, gaining the upper-hand, but the Miners then reawakened Xorr itself, which extruded a great crystal column (which contained the captive Sif and Karnilla) through the asteroid's surface, and it warmed the Asgardians that if he tried to interfere with their mission, that he would die immediately; although tomorrow, "you  -- and all humankind -- shall fall" regardless.

(Thor I#215) - Xorr incapacitated both the Gramosians and the Asgardians, who awakened in a subterranean chamber. They fought the Miners again, but they discovered that Xorr had been mobilized by another ship and was leaving. They pursued in the Asgardian Starjammer longship, but when they reached it, Xorr threatened to destroy its prisoners--Sif and Karnilla--if they resisted it further. The threat held little sway over Mercurio and his men, but Thor agreed to submit to save his lover. Mercurio cursed him as a coward.

(Thor I#216) - Thor forcibly stopped Mercurio and the Gramosians from attacking Xorr. Mercurio took his warriors and vanished, but they soon returned in spaceships and attacked anew. However, Mercurio convinced Thor that they must join forces against Xorr, and Mercurio used a rapid combination of cold and heat to shatter the section over Sif and Karnilla, freeing the goddesses. Thor then brought Mercurio, Sif, and Karnilla back to the Starjammer, where they fled in time to escape Xorr's overloading himself on the energies of a supernova explosion. Xorr exploded into countless fragments, which the Gramosians gathered up to take back to Gramos.

(Captain Marvel I#51 (fb) - BTS) - The energies of the Xorr fragments restored Gramos' polarity, saving the Gramosians. The changes returned them to peace and contentment, but Mercurio found himself unable to live with this "slug-like life...basking in the God-Jewel's rays." Over a period of months, Mercurio began organizing an invasion force to attack Earth, and he decided that the Kree Omni-Wave Projector would be the ideal weapon for their conquest.

(Captain Marvel I#51) - Mercurio returned to Earth and attempted to use a Beta-Wave Thought Processor to steal the secrets of the Omni-Wave Projector from Captain Mar-Vell, but Mar-Vell detected the scan and destroyed the processor. Mar-Vell then attacked Mercurio, who explained that he only wished to use the Omni-Wave to save his world, claiming that Xorr's energies had faded and only the Omni-Wave could re-energize them.

    Mar-Vell agreed to accompany Mercurio, but as soon as they arrived, the Gramosians ambushed Mar-Vell. Having suspected treachery, Mar-Vell was prepared and dodged the initial attack and fought off the Gramosians. Mercurio then attacked, but Mar-Vell (who had experienced the cold of space and heat of the stars) resisted his power and flattened him with a single punch.

     Mar-Vell then accessed Mercurio's Dimensional Oscillator to return to Earth, feeling that Mercurio would not come back to Earth, knowing Mar-Vell was there to protect it.

(Thor I#440) - Mercurio was one of several beings summoned from across time to battle Beta Ray Bill, Thor (Masterson), and Thor (Dargo Ktor). Though Masterson was inexperienced against Mercurio's power, the Gramosian was dazed and sluggish from his trip through time, and he quickly fell in battle.

(Quasar#14 (fb) - BTS) - At some point, Mercurio became a prisoner of the Stranger and was held within his laboratory world.

(Quasar#14,[15],16) - Mercurio was summoned by the Over-Mind, mentally enslaved, and sent to battle the Stranger and several heroes opposing the Over-Mind. Mercurio dropped Lady Lark/Skylark with a heat blast, but was then quickly flattened by a series of punches from the Whizzer of Earth-712.

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(Maximum Security#2) - During the events of Maximum Security, Mercurio was one of the extraterrestrial criminals banished to Earth.

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(Captain America III#36 (fb) - BTS) - Mercurio determined that his Dimensional Oscillator, powered by the unique sonic vibration of Captain America's Vibranium-steel alloy (see comments), would allow him to escape the barrier preventing the aliens from leaving Earth.

    Mercurio further plotted to convince Captain America to let him use his shield because his device could transport off-Earth all of the aliens recently banished there.

    Mercurio rebuilt his Dimensional Oscillator in the torch of the Statue of Liberty, presumably because this would be a significant location to Captain America and because it might help him convince Captain America that the high site was perfect for worldwide effectiveness.

    Presumably aware that Captain America would be familiar with his true identity but not that of his former host, Mercurio returned to the form of Karl Sarron.

    Armed with an energy weapon, Sarron awaited Captain America near Avengers Mansion.

(Captain America III#36 (fb) - BTS) - When Cap arrived and encountered a group of aliens, Sarron used a miniature, rifle-sized version of his Dimensional Oscillator to send the aliens off Earth, after which he introduced himself and told Cap that he could rid the entire Earth of these aliens.

    Sarron then elaborated that he could use his Dimensional Oscillator to banish all of the aliens from Earth, though he required the energy of Cap's shield to do it (see comments).

    Cap, suspecting a trap, accompanied Sarron to the Statue of Liberty and allowed him to plug his shield into his Dimensional Oscillator, but he also positioned himself to get free if anything went awry.

    As the device charged, Sarron revealed his true identity as Mercurio and tried to destroy Cap.

    Avoiding his blasts and fighting back, as the energies threated to destroy the Statue of Liberty, Cap tore his shield from the oscillator and leapt free of the Torch.

    When Mercurio pursued him, Cap struck Mercurio with his shield, and the energies in the shield caused a feedback that seemingly caused Mercurio to explode.

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(Maximum Security#3) - Mercurio was apparently one of the aliens who joined the Avengers and other heroes of Earth in fighting the forces of Ronan and the Ruul/Kree to end the aliens' banishment to Earth.

(Venom: Space Knight#4 (fb) - BTS) - Gramos required vast quantities of energy to survive. When the Gramosians refused to take the energy from other planets, Mercurio went rogue and began amassing weapons and power from "all over the galaxy."

(Venom: Space Knight#4 (fb) - BTS) - Mercurio and his people raided the planet of the Ruu'lto, kidnapping its greatest warriors and extorting them all into criminal life presumably via threats to their friends and/or family.

(Venom: Space Knight#2 (fb) - BTS) - Mercurio's agents placed a drill on the "outer rim" world of the P'qui. This displaced the normally docile Fmora from their homes and took away their food, causing them to prey on the P'qui.

(Venom: Space Knight#3 (fb) - BTS) - Mercurio's agents sent a device to the world of the Wugin and Underdwellers, and it entered their Great Eye volcano, causing its eruption. The Underdwellers blamed the Wugin and attacked them.

(Venom: Space Knight#2 (fb) - BTS) - Mercurio's agents captured and contained a number of beings in holding cells.

(Venom: Space Knight#4 (fb) - BTS) - Eventually, Pik Rollo -- controlled via Mercurio's possession of her daughter, Hilla -- was all that remained of the captured Ruu'lto.

(Venom: Space Knight#1 (fb) - BTS) - Mercurio's agents apparently employed Kio to purchase (from Gholar on a planet whose name Flash Thompson could not pronounce) a group of aliens from whose blood the drug YT-19 was created.

(Venom: Space Knight#6 (fb) - BTS) - Mercurio used stolen ships, robots, etc. to build his armada.

(Venom: Space Knight#1 - BTS) - Venom (Thompson) -- drawn to the conflict by mental voices in his role as Agent of the Cosmos -- saved the aliens (Cora and her wife and children) and cast Kio into space where he was consumed by were-fish.

(Venom: Space Knight#2 - BTS) - Venom was drawn to the P'qui, and he had his ally the robot 803 remotely (from their orbiting ship) destroy the drill.

    Fellow Klyntar/Agent of the Cosmos Myntril informed Venom that whoever had left that drill had not been sanctioned by any known empire but were rather rogue parties...and that they had been the same parties that had tried to obtain the YT-19.

(Venom: Space Knight#2) - From whatever partially destroyed world/moon on which they had established a base, Tubin reported that their drill in the outer rim had been destroyed. When Mercurio commented that the life on that planet could not have overcome the drill's automated defenses, Tubin confirmed this to be correct, and Mercurio asked who had done this to them. Tubin noted that they believed it was the same interloper they had encountered before (presumably indicating the being who had intercepted the YT-19 shipment), a Klyntar-bonded human who called himself Venom.

    Mercurio noted that they had a lock on their target's ship, and Tubin asked "Lord Mercurio" what were his orders; but Mercurio advised Tubin that he was no lord, not until they had taken back their planet. Regardless, he asked who was the worst, most vile creature in their holding cells, and when Tubin informed him that it was Pik Rollo, Mercurio instructed Tubin to place Rollo on their fastest ship and command her to bring him the head of the so-called Venom...

(Venom: Space Knight#4 (fb) - BTS) - Calling Venom "the usurper" and accusing him of having harmed his plans, Mercurio sent Pik Rollo to collect Venom's head.

(Venom: Space Knight#3 - BTS) - Drawn to the world of the Wugin and Underdwellers by the voice of the Cosmos, Venom destroyed the Gramosian device within the Great Eye.

(Venom: Space Knight#3) - A Gramosian ship approached the Wugin planet just after Venom's ship departed. They reported his departure to Mercurio and then confirmed his query that the seed they had planted there had been destroyed. Mercurio denied their query of whether they should replace the seed, and he instead instructed them to purse the Agent of the Cosmos. When a Gramosian aboard their ship reported that Venom was headed for the pleasure planet Xffgath, Mercurio ordered that they follow him and then unleash Pik Rollo.

(Venom: Space Knight#4 - BTS) - Pik Rollo shot Venom's ship, causing it to crash on the planet of the Bhiv, after which she landed on that world and attacked Venom, telling him that his head belonged to Mercurio. The fight was interrupted as both were incapacitated and captured by the Bhiv and brought before their master. As they were sent into gladiatorial combat, Rollo revealed that Mercurio held her child and subsequently shared how she had fallen under his control. Ultimately, Rollo agreed to Venom's proposition to go after Mercurio together and to rescue her child, and Rollo destroyed the Bhiv's master, leading the Bhiv to praise them as their new masters.

(Venom: Space Knight#5 (fb) - BTS) - Unbeknownst to Pik Rollo, Venom obtained back-up aid from the Iqa and the Wugin, as well as the Bhiv.

(Venom: Space Knight#6 (fb) - BTS) - The Wugin and Bhiv attacked the Mercurians, aided by 803 via their starship's weaponry.

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(Venom: Space Knight#6) - Recovering, Mercurio instructed his soldiers to kill Venom and Rollo, at which point Flash revealed the involvement of his allies, who took down Mercurio's armada.

    Mercurio credited Thompson's planning as he attacked Venom and then mocked the symbiote as being useless and weak for not taking what it wanted. In response, the symbiote battered Mercurio, ignoring Flash's instructions to stop.
    It only stopped when 803 projected a loud instruction to stop.