3. Surtur (Thor: Ragnarok, 2017)
At the end of Thor: Ragnarok, we got to see the real power of Surtur. Loki threw his crown into the Eternal Flame, and he grew into a giant. He would then use his Twilight Sword to kill Hela and destroy Asgard. In this form, there are very few beings in the MCU that could kill the fire giant.
We already know he would destroy Hela. If Surtur went up against Ego The Living Planet, it would also be no contest. The giant demon would stick his sword right through Ego’s whole planet that would destroy his heart. This is why I have Surtur as my third strongest villain.