During each of your turns, you may play up to one permanent card of each permanent type from your graveyard
This means you could potentially mill your opponent out completely based off of the amount you're willing to pay for X
This will change if spirits or a go-wide-style fliers deck ever becomes a thing, but for now Id stick to playing Collision // Colossus
There are three SpongeBob Secret Lairs, two of which are more in line with what you'd expect from a Universes Beyond product
An un-keyworded version of skulk appeared as the first level of the Ring Tempts You mechanic from the Lord of the Rings Magic set
The cards in the other four drops that are part of the Secret Lair x Dungeons & Dragons 50th Anniversary Superdrop are yet to be revealed, but they are titled Astarions Thirst, Karlachs Rage, and Death is in the Eyes of the Beholder I & II