Don't forget about the Masked Vapor deck that was used a while ago. Just don't summon both on the field. summon the 2nd Vapor on the last turn. Vapor can't be destroyed by Yubel.
You'll want to keep just 1 Vapor on the field until the very last turn, where you'll be summoning both a second WATER Hero to be Mask Changed, AND Vassal.
If you summon the second Vapor one turn before Vassal, you risk both Vapor getting Lava Golem'd.
Yeah just checked my deck and I do have double summon. I run 3 Ocean's and 3 Mask Change just in case of Ultimate Providence. Will try to bait Ult. Prov. with Good Housekeeping and jars of Greed. Also, 2 Magical Mallet's and 1 Balloons. 1 Trunade at the end will also bait U.P.
You do need Double Summon, do you even read my whole post? You must have only 1 monster on the field until the very last turn, having 2 monsters on the field before the last turn is just asking to get Golem'd.
Meaning you need to Normal Summon the second WATER Hero (you can't Mask Change into a 2nd Vapor without one), AND Normal Summon Vassal on the same turn.
from my experience, it's extremely rare to see Yubel summon Ultimate Nightmare. Usually she discarded Tribute to the Doomed/Dark Hole as Ult. Providence's cost to negate my spare Spell, so she can't destroy Incarnate with it to summon Nightmare. Or she use it to destroy her own base Yubel, instead of Incarnate.