Fist of all - quests.
Like Ezra one with cerebral trauma psi. But in same time quest must show method how realizate it or just be maximum atmospehric.
For example - termo aura. Show some burning comlex or settlement, where you only way to survive - move fast and go sometimes throuth fire. Show in dialog, what fire almost step like human and haunt character. And in end some philosopic ending. Will be this fire own wish, or viev of soul of character. Or maybe other leviathan.
Now abouth new methods - in underrail character may know some abouth past, abouth mytagens and others stuff, but mostly it is never helps again, just for 1 quest for all game and maybe for some tolk in end of game. I think will be good idea, change backstory of hero - like for scientist, or doctor will be helpful some mutagen research data for new stuff and psy. And psy good conect with it.
Like psy lightning - maybe character with high medical and psy skill will understand how posible keep some electro charges in own body and dont die in process. And idea for it, may come in moment when character read or just cook eel, or examine/take samples of coil spider.
Plus i think will be good adition if in dialog's will be used some unepected ways to use of using psi. Maybe throudh some dialoges will be opened some psi, becouse enlightment of character. Like oportunity tolk not only with high ones, but leviathan as well.
And lastone. Psy eye, or second second sight buff of juice maybe will be a key to obtain new psy abbility.