To a siegehorn, there is no such thing as a dead end.

Siegehorn Ceratops

Enrage — Whenever this creature is dealt damage, put two +1/+1 counters on it. (It must survive the damage to get the counters.)

Rivals of Ixalan Promos

Rivals of Ixalan

Enrage — Whenever Siegehorn Ceratops is dealt damage, put two +1/+1 counters on it. (It must survive the damage to get the counters.)

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.