Cheapest priced copy (Ikoria: Lair of Behemoths): $0.35 at Card Kingdom, near mint, their price list as of .
Auspicious Starrix 
Creature — Elk Beast · 6/6 · Uncommon · Ikoria: Lair of Behemoths · #294
Mutate {5}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Whenever this creature mutates, exile cards from the top of your library until you exile X permanent cards, where X is the number of times this creature has mutated. Put those permanent cards onto the battlefield.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ikoria: Lair of Behemoths | 144 | Uncommon | $0.35 | $0.49 |
| Ikoria: Lair of Behemoths | 294 | Uncommon | $0.79 | $1.49 |
5 rulings from Wizards of the Coast
- 17 April 2020If an Aura is put onto the battlefield without being cast, the Aura’s controller-to-be chooses what it will enchant as it enters the battlefield. An Aura put onto the battlefield this way doesn’t target anything (so it could be attached to an opponent’s permanent with hexproof, for example), but the Aura’s enchant ability restricts what it can be attached to. If the Aura can’t legally be attached to anything, it remains in its current zone.
- 17 April 2020If there are fewer than X permanent cards in your library, you exile your entire library and put the permanent cards in it onto the battlefield.
- 17 April 2020Any cards that you exile but don’t put on the battlefield for any reason (for example, because the card is an instant card or an Aura that can’t enchant anything) remain in exile.
- 17 April 2020An Aura being put onto the battlefield this way can’t enchant anything else that is being put onto the battlefield at the same time.
- 17 April 2020Auspicious Starrix’s effect doesn’t count as playing lands. It can put land cards onto the battlefield even if it’s not your turn or if you’ve already played your land for the turn.