I chose Pixaki because it had a lot of features (animation, rotation of layers, etc.) and it's on iPad, meaning I can draw wherever. Same goes for Procreate. Although, I do want to get into Aesprite, which could pair well with Pixaki as the latter can be exported into Aesprite. Plus, the newest version includes the power to make tilemaps like Pyxel Edit.
The crossover you described would be pretty cool. We just first need to actually finish the games (Though I have no doubt he'll finish it well). I wonder if this post will somehow reach Mark one day.