Piggy is a hostile NPC in Lakeview Cabin IV.
Piggy spawns in the slaughterhouse and is the only NPC in there. He appears to be sleeping until a playable character moves in his room or uses one of the secret doors to enter. Once awake, he will leave the slaughterhouse, ignoring all traps and avoiding trapdoors. Instead of opening doors in his path he chainsaws them open, serving as a warning that he is about to enter. It is nearly impossible to complete LVC IV without waking Piggy as he guards one of the gas cans - but if you are lucky enough to get a gas can from the secret gift room you can avoid the slaughterhouse entirely.
His movement pattern is fixed: once leaving the slaughterhouse, he runs either left to the exit and then right, or he can go right without checking left, killing any character he encounters along the way. At the far right of the level he falls into the trap hole (without taking damage) and breaks down the trap room door. If the alarm has been previously activated, Piggy will damage (but due to her high health he will need to visit the basement a lot to actually kill her) the machete-wielding woman roaming the basement. He will then leave the basement, destroying any doors in his way. NPCs outside their idle position (roaming their room) will be damaged (or killed if they were damaged before) by Piggy. He then exits the mansion, proceeds to run to the right again, and falls into the trap hole before repeating the process.
Piggy is faster with far more health than the player characters. Fighting Piggy while he is awake and chasing you is suicidal: his chainsaw has greater reach than any melee weapon and it kills in 2 hits. The easiest way to kill Piggy is to lead him into a bear trap and attack him with, preferably with a high-damage weapon, such as chainsaw or drill. It is important to kill him the first time before he recovers, as bear traps break easily. Another easy way to deal with him is to use the hypno wheel and throw stuff at him. Keep in mind that piggy is unaffected by fire.
When killed, his body, unlike any other, rolls in the direction thrown. Also, unlike other bodies, it cannot be used as a throwing weapon.