The difficult thing about making superheroes is unmistakably deciding how far their powers can go. Although nobody wants to make a hero so powerful that nobody is interested in them - like the unfortunate case of Captain Atom - you also want to create a character with dynamic and exciting enough powers that people actively look forward to seeing them used.
While generally the route best traveled is to give a character one power at a reasonable level, there are those creators who decide to go above and beyond and pump their hero full to burst with the universe's best and strongest powers.
It's a dangerous gambit, as too many powers can easily ruin a character, but it also has the potential to explore some really interesting territory in regards to humanity and how it can be affected or unaffected by having the abilities of an actual god.
Whether this be through binding them to a celestial being, giving them an inability to die, or just straight up having the most physical prowess of the entire comic universe, there are practically endless ways to make a character overpowered - although there are significantly fewer ways to take overpowered characters and make them engaging.
While Deadpool is perhaps not the first character that comes into your mind when you think of overpowered characters, that's because characters with solely regeneration powers are underappreciated for how terrifyingly powerful they can be.
Deadpool is different, admittedly, as his immortality doesn't come with a catch, or a specific loophole or weakness, but rather the simple ability to never die. It's almost always played for laughs - right up until the Deadpool kills the Marvel Universe series, where suddenly it becomes a whole lot clearer how overpowered this can make Deadpool, because it leaves him able to kill pretty much anyone given enough time and the right tools.
Add to this figures like Thanos and Man-Thing that Deadpool could viably defeat, and suddenly the combination of immortality and regenerations powers seems pretty solidly OP - or at least definitely enough to make you reconsider how you view the Merc with a Mouth.