Massive hammers were used to seal the Titan in its crypt. Requiring the strength of multiple Guards to swing true, these tools have not been moved since their last use.
Surgestone is effective on Crypt Builder because its damage is raised to 160 thanks to Attuned, allowing it to KO late-game heavies.
Powerstone is also an option on Crypt Builder because its damage is raised to 110 thanks to Attuned or 160 with 2 of them. This can be better than Surgestone if you have a lot of card draw and need to play this card multiple times.
1 or 2 Emberstones are also an option on Crypt Builder if you do not have the ability to reliably discard them, allowing them to be easily played. However, without a source of Magic Power, the damage of Crypt Builder will not scale well to lategame, so you'll need to take advantage of its ability to push heavies to the back or have some other source of Magic Power.