Cheapest priced copy (Dominaria Remastered): $0.49 at Card Kingdom, near mint, their price list as of .
Triskelion 
Artifact Creature — Construct · 1/1 · Rare · Magic 2011 · #218
This creature enters with three +1/+1 counters on it.
Remove a +1/+1 counter from this creature: It deals 1 damage to any target.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
14 printings · $0.49 to $199.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fourth Edition Foreign Black Border | 354 | Rare | — | — |
| Fourth Edition | 354 | Rare | $5.99 | — |
| Antiquities | 73 | Rare | $199.99 | — |
| Duel Decks: Elspeth vs. Tezzeret | 57 | Rare | $0.69 | — |
| Dominaria Remastered | 236 | Rare | $0.49 | $0.49 |
| Dominaria Remastered | 389 | Rare | $0.79 | $0.79 |
| Dominaria Remastered | 452 | Rare | $0.49 | $0.79 |
| Magic 2011 | 218 | Rare | $0.59 | $1.49 |
| March of the Machine Commander | 387 | Rare | $0.49 | — |
| Mirrodin | 269 | Rare | $0.69 | $9.99 |
| The List | M11-218 | Rare | — | $0.59 |
| Renaissance | 162 | Uncommon | — | — |
| Rinascimento | 142 | Uncommon | — | — |
| Secret Lair Drop (Krang's Android) | 2371 | Rare | $5.49 | $6.49 |
2 rulings from Wizards of the Coast
- 8 December 2022If you activate the ability of an attacking or blocking Triskelion during the declare blockers step, it will deal less combat damage as a result. If you wait until the combat damage step, but Triskelion is dealt lethal damage, it’ll be destroyed before you get a chance to activate its ability.
- 8 December 2022If Triskelion has damage marked on it, activating its ability may cause that damage to become lethal. For example, say a Triskelion with two +1/+1 counters on it has been dealt 2 damage earlier in the turn. If you activate its ability by removing a +1/+1 counter from it, it now has 2 toughness and is destroyed as a state-based action. You won’t be able to remove the other +1/+1 counter from it to activate its ability again. The first activation of the ability will still resolve.