My bet would be either:
1) a new clan(dark clans, pokemon TCG have dark pokemon in it ) This would be an addition to the nightmare pack which was in the past. Who says that the portal have to be green to follow the comic?
2) Sigmund returning like how kiki returned. Maybe better stats seeing the first one was pretty useless.
Collectors most unlikely. UR staffs never give out tips on who is the next collector. By assuming that lilith is the next one due to this is highly unlikely.