Interesting. Strongly suggest "you may" on this one though, or you'll kill yourself in multiplayer with it. Oh no, wait, it's only the ones you control; so it won't fire off all over the place, and you can just, um, stop dealing damage. Still a problem, but less so.

Honestly, I'm really worried about the power level on this one. Lightning Bolt turns into Ancestral Recall, which turns into a couple Lava Spikes which turn into a couple more Ancestral Recalls.

It doesn't even care where the damage goes, so painlands like Shivan Reef and Barbarian Ring compare to Library of Alexandria, while Char and Psionic Blast are practically like you've unbanned Wheel of Fortune or Timetwister. Pyroclasm and Flame Rift are downright terrifying, especially in a large group game.

You don't really need a group game to deal a lot of damage to a lot of creatures. Play a weenie horde deck and Pyroclasm your own board. I can think of worse ways to get to Dragonstorm.

That said, I like the card, and I like the mechanic. If this card limited to Skim 2, I think it would be a pretty cool engine without enabling back-breaking Earthquakes. And, yeah, adding "Deals damage to an opponent or a permanent he or she controls" probably makes sense. Triggering off of every pain land you control doesn't sound very fair.

This followed by Cave-In is particularly nifty.

Yeah, I modelled it after Tamanoa, but card advantage seems to be more powerful than life gain. Go figure. I'll edit it at some point to make it more fair.