Backup Singers are human ghosts located in the Opera Hall in Return to Karazhan.
- Firelands Portal — Rips open a portal to Firelands, inflicting 449999 Fire damage to all players within 100 yds. This calls forth a random minion of Firelands for 45 sec.
- Purify — Dispels a magic effect from friendly targets within 10 yds. The caster then draws a card, whatever that means.
- Burn, baby, burn!
- How tragic!
- I love portals.
- Oh my!
- Oh no, bad times...
- Oh no, I can't look...
- Watch out!
- You called?
- The Backup Singers are a reference to the Hearthstone adventure One Night in Karazhan.
- The Medivas were originally introduced as a trio of characters featured in the promotional material for One Night in Karazhan before later making in-game appearances in the Party Portals! Tavern Brawl. Most of the Backup Singers' quotes are references to lines spoken by the Medivas in Party Portals!.
- Firelands Portal, widely considered one of the more powerful cards from the adventure, is a mage spell which deals damage to a target enemy and summons a random 5-Cost minion for the player.
- Purify is a priest spell which has the effect of Silencing a friendly minion and drawing a card. The card was widely mocked by Hearthstone players for being one of the worst cards in the game and for being released for a class that was already considered weak at the time.