Look out…from below!
The flavor win here is not going to go unnoticed. Each tremor of this card gets progressively worse—until the giant lizard emerges from the ground and destroys everything! It might not be the most obvious, or even important, but I think it’s really great card design.
So, Subterranean Tremors is a red mass removal spell in a small but effective line of successful removal spells. The fact that this card can destroy multiple permanents at once might prop this up as useful at the very least. Certainly players that use red in casual/Commander settings will appreciate this card greatly. They were already using the likes of Earthquake and Rolling Earthquake.
There’s some real downside here that could affect Subterranean Tremors’s appeal and desirability. Unlike EDH favorite Vandalblast, this card destroys your artifacts as well. It also doesn’t hit players—which is a big deal since it can’t deal with planeswalkers like its predecessors.
Another glaring issue is if your EDH list contains specific cards such as Sol Ring and/or Thran Dynamo to ramp (which they most likely do). Is trading a board wipe (which destroys opponents’ copies) along with an 8/8 lizard a net positive? I’m not entirely sure yet.
It would probably be less problematic if one is using a deck based around Daretti, Scrap Savant where recurring artifacts is no big deal. It really all comes down to your deck needs, and which specific commander you plan to use Subterranean Tremors with. I just wanted to point out that there’s potential downside to this card if used as just a board clear—its predecessors that I named earlier are likely better for that.
Considering it’s a highly situational card, I doubt there will be much desire for folks to acquire this card with great haste. I suspect these will be readily available after a short while once Conspiracy: Take the Crown is released, and players shouldn’t have an issue finding these.
Even at mythic, I doubt the card can retain much value given how accessible the product will be to the playerbase. I think I’m okay throwing foil copies of the card in the same category here. My advice is absolutely to wait to acquire copies.