Shadowverse

I think that for Haven or Stronghold, the need for a Bahamut is very questionable, if it's needed at all. It might make sense to include it in a Sylvan deck, as it's quite controlling, and all the "good" controlling factions (except Necropolis) counter Bahamut, but I don't have room for it there.
And yes, Sybil doesn't compete with Ferwor, but complements it. Ferwor is a "round 5 where you do nothing," while Sybil is a round 5 unit with good stats that can be evolved and traded, and any opponent who leaves it on the board doesn't respect themselves.