They are the only Spirit Monsters that can be Special Summoned under any given circumstances, in which case it does not trigger their effect that returns them to the hand
The Core by Piotr Dura Descend is a new keyword introduced in The Lost Caverns of Ixalan that's actually three mechanics in one
Riftbound Origins was reviewed with a copy provided by the Publisher over the course of 20 hours of gameplay - all screenshots were taken during the process of review
It is the perfect hour for a bit of revenge
However, if you have cards in protective sleeves or, even better, unopened packs, you might have some near-mint condition cards that are more valuable than their damaged counterparts
But Clues themselves are undersupported as a main mechanic, and playing cards to take advantage of them (or even commander damage in UB) means playing cards that are pretty bad