Wicht Warden (WW2): Complete all main Easter eggs.
Nacht Raider (BO6): Enter prestige 1.
Zombie (AW): Complete 10 waves on the Riot map in Exo survival.
I think these are amazing rewards for challenging tasks (with exception of BO6, that’s not very difficult), my favourite has to be the Wicht Warden for the detail and gore.