Red Pikmin special abilities:

-Fire immunity

-Ability to walk on lava

-1.5 damage multiplier

Red Pikmin Special Commands:

-Thrown on fire: By throwing a red Pikmin to fire or soul fire it will start to extinguish that and all nearby fires.

Red Pikmin's most defining trait is their fire immunity, neither fire nor lava is an impediment for them, Being able to traverse the latter as well as striders do, which is good for retrieving your netherite gear after falling in a lava pond. 
And when you could argue fire immunity is not that useful outside of the hot nether, luckily that is not the only department where Red Pikmin excels, being the second best type for single, while doing 3 damage instead of 2 may not seem like much, is enough for a single red Pikmin to solo an unarmed zombie, and if you stack many of them in a single enemy the damage ranks up way quicker, even melting an iron golem's health in matter of seconds.
