This becomes a bit lengthy here, but everytime I post something I get new ideas :) to create game graphics you could also use vectornator, procreate, inkpad, pixelmator, graphic and artstudio. I only use vectornator, as it's fairly simple to use and generally flawless but still full of features (and the support is very active, so you can suggest new features that actually get added in the next update). But if you have a new iPad, get affinity photo, it really is the best you can get. Be sure to check the compatibility list in the app's description.