Cheapest priced copy (Eternal Masters): $3.49 at Card Kingdom, near mint, their price list as of .
Xantid Swarm 
Creature — Insect · 0/1 · Rare · Scourge · #135
Flying
Whenever this creature attacks, defending player can't cast spells this turn.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $3.49 to $89.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Eternal Masters | 193 | Rare | $3.49 | $4.99 |
| Scourge | 135 | Rare | $10.99 | $89.99 |
2 rulings from Wizards of the Coast
- 8 June 2016The defending player may cast spells before Xantid Swarm’s triggered ability resolves.
- 8 June 2016In a multiplayer game, only the player Xantid Swarm attacked is affected. Other defending players may cast spells.