I've been thinking (a lot)about a Terraria/Aveyond crossover, and I honesty believe that the idea is amazing. For example, a new Aveyond game featuring multiple weapons, items, enemies, and bosses from Terraria could be created (smashing Ahriman with a terra blade? Sounds awesome), while a new Terraria update featuring many items, NPCs, bosses, weapons and accessories (using a Sword of Shadows to destroy the Moon Lord, anyone?) could be implemented. This could also bring a lot of attention to the Aveyond games from Terraria's (massive) playerbase, as it is a relatively little-known franchise.