Kid Icarus

Without a doubt Nintendo R&D1's greatest achievement on the NES, deceptively disguising itself as a straightforward tough platformer in early levels but hiding both its Metroidvania-style boss fortress levels and its awesome character-building RPG mechanics. As you multiply Pit's health bar and strength many times over, obtain spinning shields and long shots and fire arrows and the ability to fly back from fatal falls, the game becomes more fun the more powerful you are.

too difficult to beat but cool mechanics at its time

Why did I remember this as being good?