In Co-op mode, Marc's REC stat is increased from 5 to 6, due to her base ATK of +1. Marc's passive does not change.
Marc's Hyper, x16 Big Rocket, does not visibly change in Co-op, but has a slightly different effect. The Hyper can only target enemies and not players, but otherwise functions the same as in Normal mode.
Marc's passive and Hyper are unchanged in Bounty Hunt mode.
Marc's base stats give her 34 starting stars and a markup of +15% at shops.