A yukkuri inflating its body as an intimidation tactic (similar to puffer fish without the spines). Only works against other yukkuris, won't work against humans or any other animal. Even against other yukkuris it usually only works against koyukkuris. Against older yukkuris it often just angers them.
Yukkuris will puff at anything that doesn't let them take it easy, even inanimate objects (e.g. if it's raining the yukkuri may puff at clouds).
Some yukkuri delusionally believes that puff-puff can actually deal physical damage which is obviously not true.
While yukkuris will often flaunt puff-puff as their "strongest ability" most yukkuri seems to only use it as a last resort. If a yukkuri has another way to fight such as fangs of a stick they will use that instead. Even unarmed adult Marisas will often prefer a body tackle over puffing up