head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Optimization · Practiced Mastery
Breezy open-world adventure romping through Greek myth puzzles and monsters.

Optimization · Pure Optimization
A scripted RPG where pattern-learning and pacifist routing carry you.
Immortals Fenyx Rising leans Optimization (Practiced Mastery); Undertale leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Immortals Fenyx Rising
Dodge timing and aerial combos
Undertale
Bullet-hell dodging in scripted patterns
Undertale leans a little harder on reads, though the gap is small.
Immortals Fenyx Rising
Mythic beasts follow fixed movesets
Undertale
NPCs follow fixed dialogue trees, not adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Immortals Fenyx Rising
Little randomness in the open world
Undertale
Minimal randomness in encounters
Undertale leans a little harder on optimization, though the gap is small.
Immortals Fenyx Rising
Vault puzzles, gear builds, and stamina routing
Undertale
Learning fixed boss patterns and mercy routes wins
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.