Yanappu is Dent's best and only Pokémon; it made its first appearance in BW005 where he showed it to Ash who scanned it on his Pokédex before battling.
Yanappu was the third and final Pokémon Ash faced in his Gym battle, where it went up against Ash's Mijumaru. However, Yanappu dodged all of its attacks with ease and hit Mijumaru quite hard with Bullet Seed and Bite. After Mijumaru finally hit a midair Yanappu with Water Gun, Yanappu started charging SolarBeam, which petrified Mijumaru with fear.
It is set to appear in BW006.