Death singer could be, kill all knights than her. Crota could be, kill the boomers, summon the witches and kill witches before hitting crota. VOG Templar no teleport Atheon, no time vengeance. If who ever is teleported doesn't kill the oracles and just run through the teleport the team will not wipe but you will not get time vengeance.

Templar will probably be no teleports, crota maybe a different sword bearer everytime or no oversoul. Deathsinger has got to be time (can't really see another way you can beat her). Atheon is the mystery I really don't have a clue what they will do with that fight.

I think the crota challenge will be similar to the warpriest challenge