The Super Studio games (Frozen 2, Incredibles 2, Mickey Mouse & Friends, and Princess) all use WET erase markers. Using any other kind of marker will ruin the Sketchpad. Need or want more of these markers? Osmo sells an expansion pack of Super Studio markers on PlayOsmo.com.
The Monster game/Creative Set uses DRY erase markers. Need more markers? Any dry-erase or liquid chalk marker will work just fine.