Herald Volazj is a unique card. His battlecry is to create 1/1 copies of every minion on your side of the board. This is useless unless you have minions with very strong passive effects. Yet when put into practice, this minion can really change the tide of a battle.
The best minion to combo Volazj with is without a doubt Emperor Thaurissan. Thaurissan has a passive effect that lowers the cost of a card in your hand by 1. This effect can be stacked if multiple Thaurissans are on a board. That being said, combining that again with Brann Bronzebeard, you could decrease the cost of cards in your hand by three mana per turn. Two turns on the board and you could play just about any card you wanted at any given time.
Volazj is also great to combo with Prophet Velen. With him even being another Priest Legendary, that’s a super feasible option. You could have a mind blast cost a mere 2 mana and deal 20 damage in one fell swoop. That late game play would actually shatter the entire match. With aggro decks being on the rise, removal spells are surprisingly less common these days as well, so it’s easier to keep big minions on the board.
If you’re interested in finding Herald Volazj, he’s a legendary in the new Whispers Of The Old Gods expansion, so either get him from a pack, or you can craft him for 1600 dust. Either way, he’s an interesting card for a new, niche kind of Hearthstone deck.