Some people may have discovered, equipped with tips This will be helpful to some people.

For trainable skills, so far I picked up speed up and speed down (No idea why anyone would NOT pick these up, they're a tremendous help for 3-medaling eventmaps and cost only gacha seeds!) and the 10% ATK buff on first round. That last one is relatively expensive at 500,000 gold, but you just can't go wrong with it. It should help my trigger-squad stay alive on future whale-maps