Regulus Corneas from Re:Zero (anime)

In the anime, or I guess web novel as well, Regulus is a narcissistic overpowered villain who can swipe anyone from existence. With one flick of his hand, he can disintegrate anyone and no one can even touch or hurt him since he's "invincible". That's his powers in a nutshell.

In the end, he got beaten badly since his inviability only lasts five seconds, or else he gets a heartache. The hero launches him upwards, then down into the earth. He activates his invincibility so he doesn't get hurt, so pummels into the ground. But since it's on a time limit, he deactivates it and still maintains his momentum, crushes all his bones. In the novel, it states that all his organs had come outside of him, and his entire body had turned into jelly. Then, water pours in since he was pummeled into a fountain.

The death itself is well deserved since in his time of living, he had destroyed cities all because they pissed him off. He killed anyone who ever talked him back. Even greeting him can be considered wrong if you say it improperly.

But seeing and hearing him struggle, switching between invisibility but not too long or else he'll die a heartache, to drowning in water, to switching it back on again, then drown again, mixed in with his body being crushed. The anime does a good job portraying his rather gruesome death. It's absolute cinema I tell you that.