Cheapest priced copy (The List): $0.49 at Card Kingdom, near mint, their price list as of .
Siren Stormtamer 
Creature — Siren Pirate Wizard · 1/1 · Uncommon · Ixalan · #79
Flying
{U}, Sacrifice this creature: Counter target spell or ability that targets you or a creature you control.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends | 96 | Uncommon | $0.59 | $1.49 |
| The Lost Caverns of Ixalan Commander | 171 | Uncommon | $0.59 | — |
| The List | XLN-79 | Uncommon | $0.49 | — |
| Ixalan | 79 | Uncommon | $0.79 | $3.49 |
2 rulings from Wizards of the Coast
- 10 November 2020Siren Stormtamer's activated ability can target a spell or ability that has multiple targets, as long as at least one of those targets is you or a creature you control.
- 10 November 2020If the creature you control targeted by the target spell or ability leaves the battlefield, that spell or ability is no longer a legal target for Siren Stormtamer's ability. On the other hand, if that targeted creature becomes an illegal target for the target spell but remains on the battlefield under your control, the target spell or ability is still a legal target for Siren Stormtamer's ability.