2 Bjorns, mostly because other purples not named Balthazar and Costumed Tyrum are not that great (yes, not even Guardian Bat). I kept only one Kvasir and Nordri, but 2 of those in same team might be dangerous, especially if you fire both Nordris at the same target one after another.
Mist and obviously Brynhild too. Especially Mist. Stonecleave probably not. Sumle I am not fan of either. Once she gets out, Fura would be a prime candidate to keep multiple copies of.