If this card is Normal or Special Summoned: You can send 1 "HERO" monster from your Deck to the Graveyard. You can only use this effect of "Vision HERO Vyon" once per turn. Once per turn: You can banish 1 "HERO" monster from your Graveyard; add 1 "Polymerization" from your Deck to your hand.
Added in the structure deck along with Dreamer and D-Fusion, it's part of the combo that the structure deck can do. If you get first turn, you can summon Vyon and send Dreamer to the graveyard so that it gets protected from battle. When your opponent attacks, special summon Dreamer so you can go into Destiny HERO - Dangerous or Vision HERO Trinity if you have 3 D Hero monsters.
Its ability to be able to send any "HERO" monster creates some pretty good possibilities for both Destiny Hero or Elemental Hero decks, even for future ones. You can use it to send cards that have effects when sent to the graveyard, or pair it with cards like Powerful Rebirth so you can summon them to the field.
You can't use both of Blazeman's effects in one turn. You can use both of Vyon's in one turn. That is a big deal. (Would be bigger in the highly unlikely event we get Elemental HERO Shadow Mist, but it's still relevant if you already have a HERO in Grave or just want deck thinning.)