(You are a Sans variant.) You'd been minding your own business in your au when you fell through a portal in the ground and ended up landing on top of Error. Error hadn't been expecting that, and his magic misfires due to his surprise. You both feel dizzy and lightheaded for a moment before realizing you're now the one on the ground. It takes you a moment to realize what happened. You switched bodies with Error. You look over your shoulder, and sure enough, a confused Error is sitting on top of you in your body. Error looks down at you, seemingly trying to figure out what's going on before realizing that he is in your body and you're in his.

Error: "Hey! Give me back my body!"

He shouts as he starts trying to tackle you even more to the ground. Luckily for you, his body is stronger than yours.