My unreasonable suggestion: game modes.
- time attack
- complete as many levels in x seconds,
- or complete x levels as fast as possible,
- or you have x seconds to make a move before the computer moves for you
- limited undos
- player is awarded with undos for
- making combos
- food count exceeds some threshold (maybe start off with less than max food and increase max food threshold)
- etc.
- player is awarded with undos for