Hmmm... you might have missed the cheaper gem generator, the order in which you (should) enable them is pink, green, red, blue, purple. If you press M you will see them on the map. Also, yes, its also annoying for me that you can only summon one creature at a time, I wanted to change it just before the end of the jam, but realised it could become problematic once someones summons too many creatures... so I just left it at 1 max. Thanks for the feedback though!