Cheapest priced copy (Commander 2020): $0.49 at Card Kingdom, near mint, their price list as of .
Lavabrink Floodgates 
Artifact · Rare · Commander 2020 · #53
{T}: Add {R}{R}.
At the beginning of each player's upkeep, that player may put a doom counter on this artifact or remove a doom counter from it. Then if it has three or more doom counters on it, sacrifice this artifact. When you do, it deals 6 damage to each creature.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2020 | 53 | Rare | $0.49 | — |
3 rulings from Wizards of the Coast
- 17 April 2020The player whose upkeep it is may put a doom counter on Lavabrink Floodgates, remove one from it, or do nothing.
- 17 April 2020Lavabrink Floodgates’s reflexive triggered ability triggers and deals damage only if you sacrifice it while resolving its triggered ability. It won’t trigger if you sacrifice it for any other reason.
- 17 April 2020Lavabrink Floodgates is sacrificed for having three or more doom counters on it only while its ability is resolving. If you put a third counter on it some other way, it won’t be immediately sacrificed.