Let’s keep this ability explanation short and simple, capiche? Okay.
Mellow’s Device (the tablet) allows for the creation of objects made out of Hardlight (or solid holograms). They feel the same way the real thing does, but they are different structurally. Objects have to be scanned by the Device before summoning, as to keep it in its database for future use. After that, he can create summoning cards using the hi-tech straps on his wrist. Those straps are directly connected to the tablet and have full access to all of its functions. The objects are spawned in the same state that they were when scanned (so a lit campfire will always come out as a lit campfire), but sentient scanned objects always have full loyalty to Mellow. Though, he usually asks for people’s consent before scanning as that’s the sexiest thing a man can do. The objects’ lifetime before saying peace to existence is about 15 minutes. Theoretically, anything could be scanned, as long as the Device can handle it. So, no black holes or something dumb like that. Originally, Mellow simply drew what he wanted with his Core Stylus onto the Device, and it would attempt to spawn in what it thought he wanted, like autocorrect. But that was long and tedious, so he opted for the Card System because it was flashy, fun, and matched his new jester persona.