Moldstack was added in Beta 50.0. Previous Versions can be found here.
Moldstack, as one of Moldbygg's attacks, works very similar to it, being also a Mold with Taunt and a Dust to give its owner a new Mold. But instead of a Moldsmal, it will instead choose a random Mold on your board (except itself, of course). As such, if you have none, none will be given.
Compared to Moldbygg, Moldstack has -2 ATK for -2G, making it a more effective Taunt (albeit vulnerable to Muffet's Pet). However, the Mold that is given will be added to your hand rather than directly summoned, giving less board pressure as a trade-off.
Fortunately, Moldstack lacks the restriction that Moldbygg has (and even lacks a Magic entirely), making it a better monster in the case of direct summons.
- Weird Molds (by Diamaincrah)