At the time of his release, Easta Buni, along with Undead trolls, were the only trolls in RuneScape with an updated look. Since then, Trolls in Daemonheim have been given the updated look as well.
Easta Buni looks different in the Knowledge Base articleIn the Knowledge Base article for the Easter event, a picture shows Easta Buni looking significantly different from in game. The in-game model resembled a mountain troll while the Knowledge Base model resembled an ice troll.
Easta Buni is the first NPC to have a voice. A player commented on this subject and Mod Fnord replied that it was indeed a NPC voice and are hoping to have more. Voices have since been added to the tutorial NPCs, some boss monsters in Dungeoneering, Nex and Bard Roberts.
He seems to have tried to eat the Easter Bunny, as trolls are named after the first thing they ate.