Cheapest priced copy (Teenage Mutant Ninja Turtles Source Material): $1.49 at Card Kingdom, near mint, their price list as of .
Silverclad Ferocidons 
Creature — Dinosaur · 8/5 · Rare · Rivals of Ixalan · #115
Enrage — Whenever this creature is dealt damage, each opponent sacrifices a permanent of their choice.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $1.49 to $11.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Rivals of Ixalan Promos | 115p | Rare | $7.49 | $11.99 |
| Rivals of Ixalan Promos | 115s | Rare | — | $8.49 |
| Teenage Mutant Ninja Turtles Source Material | 9 | Mythic | $1.49 | $1.99 |
| Rivals of Ixalan | 115 | Rare | $3.49 | $5.99 |
4 rulings from Wizards of the Coast
- 19 January 2018When Silverclad Ferocidons's triggered ability resolves, first the player whose turn it is (if that player is an opponent) chooses which permanent they will sacrifice, then each other opponent in turn order does the same, then all chosen permanents are sacrificed at the same time. Players will know choices made by earlier players when making their choices.
- 19 January 2018If creatures an opponent controls are dealt lethal damage at the same time that Silverclad Ferocidons is dealt damage, those creatures will be destroyed before that player chooses a permanent to sacrifice.
- 19 January 2018If multiple sources deal damage to a creature with an enrage ability at the same time, most likely because multiple creatures blocked that creature, the enrage ability triggers only once.
- 19 January 2018If lethal damage is dealt to a creature with an enrage ability, that ability triggers. The creature with that enrage ability leaves the battlefield before that ability resolves, so it won't be affected by the resolving ability.