If you swing with it and the opponent doesnt block the attack, they get 2 poison counters
Where he starts to get very powerful, very quickly, is when you start casting more Hero creatures
Pikachu ex Hyper Rare (179/131) is the standout, with strong demand driven by Pikachu's universal appeal
Gisa, the Hellraiser Gisa, the Hellraiser is a good lord and source of tokens for zombie and skeleton decks, and the Cult Conscript-type skeleton in Forsaken Miner enables a grave full of synergy
You might also consider running Horn of Gondor to increase your human creature count, or Karvanista, Loyal Lupari to spread out +1/+1 counters on attacks, or even Cloaked Cadet for some extra card draw
All things considered, I think you can argue that Invasion of Ravnica is anywhere in the A- or B-tier range, although I'm going to aim high and put it in A-tier