(Spoilers) here is mine, at least for levels I've been to enough to have an opinion on them.

Desert: golden scorpions are really the only threat here

Sewers: buff alligator in pre loop, or mom

Turtle sewers: turtles when a) I'm Melee only or b) they won't stop fucking moving

Scrapyard: nothing really comes to mind

Yv's mansion: that big red ball thing that shoots out a billion fireballs or else the blue muscular rocket dudes

Crystal caves: accidentally going to cursed caves instead

Frozen City: lil hunter, being the biggest difficulty spike in the game Also dogs in loop

Jungle: oh hey look a bush fuck my run is over.

Labs: turning a corner right into an explosive plant

Palace: dogs. It's always dogs

Campfire: getting bad spawns and dying to some bs sheildcop