Fire Emblem Awakening
Classic Mode
Lunatic Difficulty
Castle Apotheosis
The Secret Battles

Six fights, no saving, against some of the absolute cheapest enemies I've seen in almost any game I remember playing. Stats higher than your maximums (I saw an enemy with 99 Luck), Skills you can never acquire (like Hawkeye: enemy attacks always hit, and Dragonskin: protects against Counter damage, critical hits, and cuts all damage in half), outnumbering you, and relentless as can be.

The further you get, the more the stress ramps up, because you never want to lose a character.

I am not looking forward to Lunatic+.