Actually picking same character is a bug, so idk if double steroids is fair

Looks like you don't even played or touched NTT at all. This mod allows to play in co-op and fixes most of the stuff that caused problems in original game. Level generation code wasn't touched at all and portals wasn't changed, it was always spawned at last destroyed object/enemy. I think you didn't even read changelogs for NTT that are included with it. Basically NTT is same as original NT, but with minor fixes that mostly covers post-loop bugs and adds in game recording and replay function, that can help a lot.