Doomsday is one of the most terrifying antagonists in the entire DC Universe, being literally one of the few characters to install fear in Superman, even outright beating him to death. Naturally, the idea of one Doomsday is bad enough, but with things like the Multiverse, there are plenty of Doomsdays to go around, each more terrifying than the last.
https://screenrant.com/10-most-powerful-version-doomsday-superman-canon-dc/