Trample Whenever a land enters, create a tapped Powerstone token. (It's an artifact with ": Add . This mana can't be spent to cast a nonartifact spell.")
Not legal in Standard, Pauper, Alchemy, Standard Brawl, Pauper Commander, Premodern, Pre-EDH, Old School
Notes & Rules Information
Sarinth Greatwurm's second ability triggers whenever a land enters the battlefield under any player's control, not just under your control.
(2022-10-14)
Powerstone tokens are a kind of predefined token. Each one has the artifact subtype "Powerstone" and the ability ": Add . This mana can't be spent to cast a nonartifact spell."
(2022-10-14)
Although all the cards in The Brothers' War that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn't part of the token's definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won't enter the battlefield tapped.
(2022-10-14)
You can use the added by a Powerstone token on anything that isn't a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.
: Add 
. This mana can't be spent to cast a nonartifact spell.")