Proper difficulty balancing or making higher difficulties more interesting than just enemies with better aim, health and damage. I think bayonetta, dmc and ninja gaiden did difficulty best and make those games super replayable as on say the hard difficulty you will fight late normal difficulty enemies earlier and replace those late ones with new tougher ones, as well as making the higher difficulty’s being more so about mastering the game and it’s combos and weapons and how to tackle different situations rather than just cheap and lazy difficulty design that a lot of games sadly do of just cranking up number and worse is not testing it and is how we get abominations and near impossible games like world at war veteran or especially halo 2 legendary