Must use same Attribute HERO monster as catalyst to Special Summon.
Important to note that Mask Change cannot be used during Damage Step.
If your targeted HERO monster leaves your Field due to other card’s effects, when Mask Change was activated, you may not Special Summon Masked HERO Vapor. Possible scenarios include Enemy Controller chained to your Mask Change, in order to take control of your targeted HERO monster.
You can use Mask Change on your Masked HERO Vapor during your battle phase, to Special Summon another Masked HERO Vapor, for possible OTK.
Where the Heroes Dwell Can be used after you Life Points are 2000 or below. Play the Field Spell "Skyscraper". If there already is Field Spell on your side of the Field, Return it to your hand. This skill can only be used once per duel.
It's because you can't read Vapor's text, apparently.
Good against Sea Stealth Attack the only issue is that it's not bigger than the Whale unless the opponent is running Legendary Ocean and not the Umi skill ... it gets to 2600 with LO with is bigger than whale but the cost is that you'd have to play either bubbleman or ice edge and both are pretty weak on their own