wow, that so reminds me of what i started in the steamgroup of touhoucraft, i hope itll turn out with a higher interest than just topaz :3
gap-block for worldchanging or as general teleporter does sound interesting. too bad i just have bad mob ideas ...
but whats more important: SPELLCARDS / spelltomes
In my opinion spellcards should be made by combining an empty spellcards with certain items, or combining certain spellcards
kinda like Empty Spellcard + Blazepowder (filler) -> fire Spellcard -> 2 firespellcards -> Fireball Spell and so on and on....
maybe a special book to make a tome that works on durability instead of uses like the spellcards do
IMPORTANT NOTE: Whatever the spellcard, i think they should NEVER damage the enviroment, even a "Nuke" spell shouldnt damage blocks, the griefing potential would be too high :)
EDIT: oh, ofc we would need new special effects/textures for the spells, mobs, areas, plants, items etc etc etc etc etc etc xD
Concerning Touhou Characters as mobs, it wouldnt be nice of real touhou fans to turn them into cannon fodder, especially the popular ones *evil smile*
(*inb4 raptorrotas cannonfodder mob*)
i think the "normal" mobs added should be fairies or minor/nameless youkai, while the characters become either midbosses or bosses. but thats just my opinion.