A Tarmogoyf is fairly unreliable threat in cube because there will be things to block it most of the time
This means that, even if you have seven cards in your graveyard when you first cast the spell, if you lose cards from your graveyard before it has resolved on the stack, like through paying escape costs or a well-timed Tormods Crypt, you could fail to meet the threshold by the time it resolves
It's an excellent source of card advantage in your manabase if you're playing at most one, maybe two colors, and it can fill in gaps for colors that don't have unmitigated access to card draw
With only one power, it seems hard to blow opponents out by flashing it in after attacks, but it might be a sideboard all-star against aggressive decks that rely on one-toughness creatures
What Is the Correct Amount of Protection for an EDH Deck
Emearld/Amethyst This is a strong matchup for you as your opponents characters will largely be fodder against your powerful retinue of songs