It's easy to cast along with its other burn partners and having multiple copies of essentially the same effect leads to all of your burn spells doing a ton of damage
And frankly, the only reason this hits back at #10 these days instead of a lot higher, is that the most commonly played multiplayer format, Commander, starts with 40 life instead of 20, so its not as painful there
Though it's got a pretty steep cost at two of each color of mana, Progenitus can be really annoying to get rid of for opponents
This is synergistic with the "flashback" and "jump-start" mechanics found in recent Magic sets (see "Preview: 'Magic: The Gathering - Ravnica Allegiance'")
Zabaz has this strange ability as a modular tie-in, but this comes up frequently with Hangarback Walker an excellent card if you can pop it on demand, and often a mediocre one otherwise