I don't know how others can practically manage to mix up to 7 TSs (assuming you have all of them) in a 30-card monster deck, but this is how I house rule the special scenario:
- shuffle a TS into the bottom 10 card with Doom beneath the deck
- create another TS pile by placing the remaining Stones there
- *whomever is ready to fight Doom, roll a d6 to determine the number of TS to bring into the dungeon. If you fail, return the TS to the pile. Repeat*
-Victory condition: defeat Doom + outnumber VPs.
I figure this might be more thematic!