Bob Parr (No modifications, or super suit) is in a silver blind bag, obtained by collecting all the minikits in Level 2: Hover Train Hijinx.
Gilbert Huph is in a red blind bag, obtained by collecting all the minikits in Level 9: Nomanisan Island.
Once you've opened the blind bags, set character 1 as Gilbert and character 2 as Bob. Then attack Gilbert with Bob.
It doesn't matter if you have the red brick Invincibility turned on or not. You just have to hit him, not kill him.