You're right; I double-checked, and the regular bomb's explosion also only deals a minuscule amount of damage to opposing players, though this is masked by the bomb itself dealing a reasonable amount of damage on contact, pre-explosion. Even if this oversight got fixed, though, I still think that having the Nitro Bomb deal recoil damage is going overboard. You didn't add any similarly-massive drawbacks for other objectively-improved versions of powerups like the long whip or the axe/boomerang sword; at most, you just gave them a cooldown period and made them rarer. You should do the same for the Nitro Bomb, maybe even limit it to being a pricey shop-exclusive item like you did with the gold leaf, but no recoil damage; that's going too far.
Anyway, I stumbled across another one: if you're one whip's length away from your opponent, you can still hit each other with a down-angled whip attack, even if you're directly in front of each other instead of below at an angle:
Weirdly, it doesn't happen if you're too close to each other; you have to be at the edge of the whip's range for the discrepancy to occur.
EDIT: I almost didn't realize your intent with the jumpthrough arrangements for Prison Maze because the Skybase tileset's jumpthroughs are just flat clouds at the top rather than being full squares that can fill out the intended wall/prison bar shapes. You did a good job at making sure all the other available themes had square jumpthroughs, though.