Cheapest priced copy (Commander Masters): $0.39 at Card Kingdom, near mint, their price list as of .
Ulamog's Crusher 
Creature — Eldrazi · 8/8 · Common · Rise of the Eldrazi · #13
Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)
This creature attacks each combat if able.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
7 printings · $0.39 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 6 | Common | $0.39 | $0.79 |
| Duel Decks: Zendikar vs. Eldrazi | 44 | Common | $0.49 | — |
| Modern Horizons 3 Commander | 161 | Common | $0.39 | $0.79 |
| Modern Masters 2015 | 7 | Common | $0.49 | $0.49 |
| The List | UMA-8 | Common | — | — |
| Rise of the Eldrazi | 13 | Common | $0.59 | $4.49 |
| Ultimate Masters | 8 | Common | $0.59 | $1.99 |
3 rulings from Wizards of the Coast
- 15 June 2010Annihilator abilities trigger and resolve during the declare attackers step. The defending player chooses and sacrifices the required number of permanents before they declare blockers. Any creatures sacrificed this way won't be able to block.
- 15 June 2010If a creature with annihilator is attacking a planeswalker, and the defending player chooses to sacrifice that planeswalker, the attacking creature continues to attack. It may be blocked. If it isn't blocked, it simply won't deal combat damage to anything.
- 7 December 2018If Ulamog's Crusher can't attack for any reason (such as becoming tapped or having just entered the battlefield), then it doesn't attack. If there's a cost associated with having it attack, its controller isn't forced to pay that cost, so it doesn't have to attack in that case either.