You might want to use KevinK's Reznor
instead as. Kevin's changes makes it so that they can be properly used outside of the arena.
However, there still is one thing to consider: The bridge. The issue with the bridge is that the game expects the tilemap to be located in the same arena as the vanilla. As you know, the arena is mode 7 so the game has to handle both, the mode 7 tilemap (always fixed to be located at the start of VRAM) and the mode 1 tilemap for the bridge. And since the mode 7 tilemap overwrites the mode 1 tilemap, said tilemap needs to be reloacted to a different position in VRAM (VRAM 0x5800 compared to VRAM 0x3000). The result is that the bridge destruction is incompatible outside of their arena.
The second issue is that the bridge should get destroyed when two
of them have been killed. The game puts them to fixed sprite slots so what might be one Reznor for one playthrough could be three Reznors for a different playthrough. That might explain why the level doesn't finish: The game expects that $151C
for specific sprite slots are one which might not be always given.
It might be a better idea to create a custom code for bridge instead.
Okay, my layout looks ugly.