With Mistral + Violetheart Pendant (fast regen combo), I "farmed" Relics. Digging down quickly on the lookout for them and restarting once out of stamina or upon hitting the Ice zone. It took hours of me breaking Relics (tfw when 7 small pings) but I finally got all 20 Relics and got the final hat.
(The flavor text for "Black Rectangle" Relic made me laugh)
The difference between Nix with 6 Power and 7 Power is massive. Just look at my remaining stamina and how my shields are still intact. 
Anyway, despite how grindy it got at the very end, I enjoyed unlocking all the cute turtles (my fav is Caela) and all their different abilities that made them each unique to play as, crafting recipes, and progressively getting to further Zones. Multiple soundtracks so you never get dull hearing a single song over and over. Solid game mechanics (I like the Sand zone best because I can "drag" a healing (sand) tile with me as an emergency heal for later). For a game about digging down it surprisingly has much depth, heh.
Thank you for creating this game! I wish you just as successful in your future endeavors!