Looking forward to this, hope its fun.
Reminds me of an old Godzilla game I used to play on the genesis or snes I believe. It was similar to this in terms of selecting from a bunch of different Godzilla characters and it even had an Ultraman like character in it (not sure if it was ultraman or not).
Can't remember the name of that game though.
edit - I finally found it:
https://www.youtube.com/watch?v=fpkyLJsiHSw
King of Monsters. It wasn't actually Godzilla, but a bunch of rip offs (Godzilla like character, king kong like character, and an ultraman rip off).
I remember loving it though.