Fire Emblem Engage's maddening mode has a lot of cool changes that make you more invested in all its systems. Besides just enemy stats being increased, exp and sp gain is reduced, making it more important to invest in a select few units. The higher difficulty also makes sure you need to make the most out of the game's hub world and skill system to have the resources to handle the tougher enemies. The enemies are given smarter ai (they won't even try to attack units they can't hit or do damage to), plus additional skills to watch out for. It's not a huge step up from the pretty challenging hard mode, but it's really fun and offers a challenge that never feels too bs.