Good ideas all around! I would suggest allowing hardcore players to "flex" a bit, either through an achievement system or a handicap setting. A casual player can play the game just fine from start to finish without having to select "easy mode" and feel like a noob, but a hardcore player can 100% or speedrun if they so choose. Beat the next level without jumping, or only using one kind of attack, or in "melee only mode". Agreeing with Afloof.dev, optional challenges that make hardcore players feel like they accomplished something, without alienating new players or making them feel like noobs.