(Headcanons belong to Rosie)

Pump

1. Pump seemingly hypnotized by Eyes 

2. Blue eyes whenever a demon is around (with the exception of Skid)

3. Suddenly has knowledge about demons' weaknesses 

4. More cautious about his surroundings (knowing that angels are vulnerable to certain things)

5. More soft-spoken in certain occasions

Skid

1. Immune to the Piper's song while Pump and the other characters aren't 

2. Not hypnotized by Eyes seemingly by how they're both demons 

3. When nearly getting holy water splashed by the Priest, Skid looked a little more startled than Pump 

4. Seemingly a little more assertive (shown when Skid spoke up first about their Happy Fella doll when they saw Roy and his friends with it after they stole it)