The King of Fighters XIII/Dark Ash
In a nutshell
Dark Ash is the final boss of the game. It is well-known across the fighting game community that SNK's bosses are known for their undisputed cheapness, and Dark Ash is no exception. He has no delay on his fireballs whatsoever, and he will endlessly spam them in an attempt to keep you out. In addition, his Germinal, which used to require the Sans-Culotte to be used and disables your specials, can now be used freely. His AI also command reads and is able to almost perfectly react to everything you do. The secret to beating Dark Ash? Sweeps. Pressure him in the corner and sweep kick him until death.