i am not, unfortunately, knowledgeable in multiple of your indie crossovers, but i am in Terraria so i will use that for examples. a few of the outfits in DC modify certain cosmetic elements, like the Modernized Bomber outfit replacing the crit sound effect with the one from Hotline Miami. however, certain items and other things actually have much in common with stuff from these games. for instance: there are numerous memes comparing the Assault Shield to the Shield of Cthulhu (i'll spare details but they're basically the same thing, minus the parry concept on Terraria's side... for now). another example: the Serenade. it's literally a floating sword that kills things for you! Terraria similarity: the Terraprisma summon! my proposal with this information (and more that you gather yourself), is to modify the cosmetic appearances and SFX of DC items that bear similarities to crossed-over games, while wearing their respective outfits. example from earlier: while wearing the Familiar Outfit, Assault Shield looks like Shield of Cthulhu (maybe is renamed?) from Terraria.
i suppose it's 
not with the Return to CastleVania DLC coming, it would be a decent time to give us non-DLC people a bit of extra cosmetic appeal to the Everyone is Here stuff (including if you can salvage SFX from the castlevania franchise)!
#superior crossover content!!
zinc robin
next aurora
i ain’t reading all that
zinc robin
that's completely fine.
stuck fog
Absolutely but a really cool idea