As with other ETB's, you want to be able to pop it back to your hand to give it another whirl. It's otherwise a 6 CMC 6/6 critter. The ETB is what matters for this card.
Sphinx of Foresight was in my starting hand for this modeled game.
Anticipate is very useful in this deck.
Tyrant's Scorn lets me pop Gyruda for another whirl.
I can sacrifice rats from Piper of the Swarm. Here, just as an example, I sacrificed Orzhov Enforcer to draw cards off Erebos.
Lazav becoming Atemsis is good. I can tap it and draw and discard.
Bloodsoaked Altar is also really good in this. I can sacrifice/discard for a 5/5/ Demon token.
Forever Young lets me make use of all of the other cards that land on the graveyard via Gyruda.
I can also have Spark Double become a copy of Piper of the Swarm.
Last, but not least, Unexplained Disappearance allows me to recast Gyruda.