Pit, to me, sounded like a squawking bird, especially his voice clip that goes something like "a-ha!" ^-^
I am not sure if this was in the previous installments but notice when you are at high percent and collided anywhere on the stage, your character makes a "grunt" or "pain" sound. In very enclosed stages, such as the lower area in Temple, you can hear characters grunting repeatedly as they collide back and forth on the stage in a pinball-like motion due to extreme knockback.
I tried this with Pit in the training mode. Take him to that underground area, set his percent high, hit him with a powerful attack, and watch him hilariously go "a-ha! a-ha! a-ha!"