Stahl is just a 3* but a good reliable low rarity tank that unironically carries and becomes a fave of the F2P group. There are videos on youtube of Stahl Solo's against top end bosses.
Arryn is the 5* waifu that is like 90% horny fan art but has lasting power so she isn't just the 'flavour of the month'. Also created with an intentionally busted kit.
Avian... I actually designed a Pokemon Masters dialogue branch as a 4*. I can share with you if you want!