HARD Mode:

Enemy HP is boosted by x 1.25, ATK by x 2.0 and DEF by x 1.25.

Enemy Panic count during attacks is lowered and some enemies can shake it off regardless if the counter is still there.

New enemies also appear in each Chapter to challenge Keldy and/or send him to his doom.

Enemies are more aggressive and may use attacks that you likely would never see in a NORMAL game.

Bosses are mostly the same, except some like Trent have added elements to the mix.

Lucre is boosted however, with x 5 multiplier during Chapters and x 10 during the medal bonus after completing the Chapter.

ULTIMATE Mode:

This should be renamed Keldy Must Die.

Enemy HP is boosted by x 1.50, ATK by x 3.0, and DEF by x 1.50.

Enemy Panic count is lowered even further and much more enemies will shake off Panic status from a relatively early Chapter.

Enemy AI is extremely aggressive and if there is a mob of enemies nearby, more often than not they will be gang-beating Keldy.

Even more new enemies show up and they are difficult to handle without a doubt. Enemy mobs are much larger in size as well, making it hard to isolate each enemy and take them down. Also, an insane amount of enemies have resistance to Mono objects compared to any other modes. A Mushboom not being affected by a barrel it gets hit by is one example of that.

The bosses gain the most benefits on ULTIMATE. Their Panic counts are extremely low, with most Panic attempts only yielding counts from 6-9 save their weakpoints(10-15). They show off new attack patterns and many of their attacks are greatly boosted with new effects apart from damage. Some transform into cheese themselves for reasons such as stun-lock(via physics) or attacking so much that it’s nearly impossible to escape once hit. Many summon loads of weaker monsters to distract and annoy you as well.

Lucre is boosted further, with x 10 multiplier during Chapters and x 100 during the medal bonus after completing the Chapter.