As for Momo's achievements, I think it's challenging. It's normal to have some of the difficult parts, isn't it? And it doesn't have to be done. It's just something you try to challenge if you have ability.Achievement,It is a thing that has challenging nature,there will be different levels of difficulty
Some thoughts about achievements - maybe some interaction? With Catera - buying, selling, identify. Kinda "make a deal" :) Teala - use her ability to teleport. And Rabbit.. well.. you know ;)
Momo's achievement is bullet-hell, but it's ok, i think - just act like Neo xD Or maybe Mofu create some items/abilities to help with this achievement ;)