Silverclad Ferocidons

If 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.

If 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.

If 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.