the game seems to handle odd-tile-width enemies just fine outside the Colosseum, perhaps because their starting X-coordinate is always on a tile boundary. so i'd leave C1/215F alone, as it affects too many things that don't need changing.
is your concern with the Colosseum horizontal centering formula: updated X coord = ( (128 - width) / 2 ) + 24 ,
allowing for a mid-tile X-coordinate when the tile width is odd?
in that case, i'd go right at the Colosseum-specific code. change C1/15C1 to:
LDA $812F (adjusted tile width of enemy from slot #0)
INC
LSR
ASL (round up to even #)
ASL
ASL
ASL
STA $10 (store width)
i'm sure you can find 3 bytes somewhere. ;) maybe the C1/15F6 segment can be shrunk by starting with B0h?
anyway, it might still be worth dissecting these spells' animation scripts to see what it is about certain coordinates that make them choke.
We have EVEN MORE themes now, but some old ones are gone...