Thanos is essentially the end boss of the Marvel Universe. Over the years, he's battled just about every major Marvel hero out there at least once and made a name for himself by trying to end as many lives as possible. As a villain, he has it all. He's superlatively powerful, extremely intelligent, and a master tactician. He's stood against some of the most powerful cosmic beings in the universe and triumphed, living up to his oft-repeated claim of inevitability.
Thanos is one of the Eternals, a powerful subgroup of humans. Created by comics legend Jack Kirby, the Eternals are nigh-indestructible and among the most formidable beings in the universe. Lately, Thanos and the Eternals have battled it out, and while Thanos has had the upper hand, some Eternals could beat him if they put their minds to it.
8 Mentor Knows More About Eternals Than Anyone
Mentor is Thanos's father and the leader of the Eternals of Titan. Mentor broke away from the Eternals of Earth because of his desire to tinker with Eternal biology and allow them to mate amongst themselves. It's because of Mentor and his wife Sui-San's experiments that Thanos even exists at all. While Thanos is much more powerful than his father, Mentor could destroy his son if he really wanted to.
Mentor understands Eternal biology in a way that few others do. Given enough time, Mentor could create a weapon that would allow him to defeat Thanos. The fact that he hasn't in all of these years doesn't mean that he can't; rather, it means he's resigned himself to being punished for Thanos's sins.
7 Zuras Could Defeat Him By Channeling The Power Of The Uni-Mind
Zuras is the oldest Eternal and has been Prime Eternal longer than any of the others. He's known for his power and wisdom, but even that didn't help him against Thanos. Thanos was able to kill him, but that doesn't mean that it would be impossible for Zuras to beat Thanos if it came down to it. In fact, if Zuras had warning of an attack by Thanos, he could use one of the Eternals' most potent abilities.
The Eternals have many secrets, and one of them is the ability of the Prime Eternal to form a Uni-Mind, combining the power and knowledge of three or more Eternals into one powerful being. The Uni-Mind is capable of amazing things, and with enough Eternals, Zuras would be able to defeat Thanos.
6 Phastos' Knowledge Of The Machine Gives Him An Advantage Over Thanos
Phastos is the technology expert of the Eternals and the inspiration for the Greek god Hephaestus in Marvel's history. Phastos' job among his people is tending to the Machine. The Machine does many things for Eternals: it regulates their cities, stores their memories, teleports them just about anywhere, and resurrects them when they die. Phastos understands it like few others, and this understanding of it would allow him to defeat Thanos.
While Phastos definitely doesn't have the power to beat Thanos, he's proven able to manipulate Thanos's very body and use it against him. With the power of the Machine on his side, Phastos could teleport the Mad Titan into the heart of a star or scramble his molecules across the Earth. Phastos could do things to Thanos that he has no defense against.
5 Druig's Mental Powers Are Greater Than Thanos' And Will Make A Huge Difference
Druig is the self-professed snake of the Eternals. Beyond the requisite Eternal powers, Druig is also the most skilled psionic talent among the Eternals of Earth. He has spent his life among them using these powers in order to gain power for himself, enacting schemes that have caused his fellow Eternals to be wary of him. While Thanos himself has some psionic abilities, he can't stand up to Druig's skills.
Like most Eternals, Druig wouldn't have a chance against Thanos in a one-on-one fight and has, in fact, been killed by the Mad Titan before. However, using his psionic powers, Druig could overcome Thanos's mental shields and do whatever he wanted. As long as Thanos didn't surprise him and Druig had time, he could enslave Thanos or destroy his mind.
4 Thena Isn't As Strong As Thanos, But She Has What It Takes To Beat Him
Thena is the Eternals' best fighter. While her strength is lower than some Eternals, she makes up for it with her cosmic energy manipulating abilities. She has mastered these powers and can use cosmic energy to form weapons that utilize her mastery of many different fighting disciplines. It's this that would allow her to defeat Thanos if it came down to it.
Thanos is powerful, but he's no master fighter. Thena has been using her Eternal abilities for eons and slaughtered entire armies of Deviants on her own, a feat made possible as much by her skill as anything else. Her cosmic energy-based weapons can burn as hot as stars. Thanos is extremely durable, but he couldn't stand up to weapons that powerful for long, and Thena's superior strength and speed would let her get in close and cut him to ribbons quickly.
3 Sersi's Power To Manipulate Matter Would Be Thanos's Downfall
Sersi is the most well-known Eternal, having left Olympia, the Eternal city, and joined the Avengers. She has all of the requisite Eternal abilities, but she has one power that sets her apart from her fellow Eternals. Sersi's psionic skills are great, but her ability to manipulate matter is greater. It's this power that would give Sersi the win over Thanos.
Sersi rarely cuts loose with her matter-altering abilities, but she could scramble Thanos's molecules with them. She could theoretically transform his organs to rocks or turn the air in his lungs into nuclear fire. She could transform his blood into the most acidic substances she can imagine. If Sersi was so inclined, Thanos would stand no chance against her.
2 Makkari's Speed Holds The Key To Beating Thanos
Marvel's speedsters can be blisteringly fast, and even among these, Makkari is considered one of the fastest. She can move at the speed of light when she needs to and still has all of the powers that Eternals normally have. That means she can hit Thanos with a million super-strong blows a minute. She can blast him with cosmic energy as she runs in circles around him. She can move faster than Thanos can even comprehend.
However, her greatest power would just be to build up to hitting the speed of light and punching him in the face. With her super-strength and the mass increase that moving that fast gives her, she would destroy Thanos with one punch. While the devastation this would cause to the area around them is incalculable, it would spell the end for Thanos.
1 Ikaris Has Everything He Needs To Beat Thanos
Ikaris is considered the Eternals' greatest warrior. His powers are pretty well balanced, and while he isn't the best at anything, he's amazing at everything. He's strong, fast, can channel cosmic energy well, and has a lot of experience and skill. He's fought Thanos and fell short, but that would only motivate him to fight harder the next time he faces him.
Ikaris is often referred to as the arrow of the Eternals; they point him at a foe, and he destroys them. While he seems like a dumb warrior type, he's a million years old and understands the need for surgical strikes. With the right preparation and mindset, Ikaris could defeat Thanos, even though there's a good chance it would kill him in the process.