Zoanthrope is probably the biggest potential monster, offering both card draw and direct damage on top of a flying creature that's slightly more difficult to kill than either Niv-Mizzet
They have three steps that represent separate chapters in a story, each with different effects in-game, like summoning creatures or dealing damage
Usually resigned to recurring utility creatures, Rally the AncestorsRally the Ancestors takes on new life in a deck like ours, where an overwhelming majority of our creatures have haste
There are a lot of Adventures in this set and doubling them is huge
Finally, the level three ability, which costs a further four mana, lets you put a +1/+1 counter on each creature any time you cast a spell
You then get to play that card for free