My Pet Monster (1986)

Max is an average underdog boy trying to fit in at school but generally being a bit rubbish. During a field trip a statue turns him into a monster. A historian named Synder captures him and his sister but they break out in time to spoil their older brother, Rod's date. The monster scares his date's poodle before the dog show. Skipping on cash they take the dog to a cheap dog salon and the owner steals it and enters it himself. Rod swoops in and stops them from taking the prize and the men are sent to jail. For no logical reason the boy is restored and after begging to the statue the film ends on Synder gaining the power of the monster.