Devil May Cry 4

Beat up to and including level 40 in Bloody Palace mode. To unlock Bloody Palace mode, beat the game on Devil Hunter difficulty. Do not quite the game, you need to die or finish all 101 floors to get the achievement. Below are a list of the enemies from waves 31-40:

31 Chimera Seed x6, Mephisto x3
32 Scarecrow x3, Faust x1
33 Mephisto x2, Mega Scarecrow x1
34 Mephisto x6
35 Mephisto x3, Frost x1
36 Scarecrow x2, Faust x1
37 Mephisto x2, Assault x3
38 Mephisto x2, Blitz x1
39 Chimera Seed x9, Faust x1
40 Bael (Boss)

complete up to floor 40 (you have to fight bael or dagon depending on the char you pick) of bloody palace
dont quit you must either get a game over or finish the palace (101) and will unlock at the results page.