After you add your "Boss", place the stage you want him to be assigned to after his name. Then place a comma followed by "order = x" (Order is when he should fight. 1 - 9. 1 being one of the first people you fight. 9 being one of the last)
[Char Name] [Stage] [When he should come]
Example : ; BLACK RUGAL, stages/mybg.def, order=9
You'll also have to adjust this ( I suggest you read and understand it as well) :
[Options]
;Here you set the maximum number of matches to fight before game ends
;in Arcade Mode. The first number is the number of matches against
;characters with order=1, followed by order=2 and order=3 respectively.
;For example, for 4,3,1 you will fight up to 4 randomly-picked
;characters who have order=1, followed by 3 with order=2 and 1 with
;order=3.
arcade.maxmatches = 6,1,1,0,0,0,0,0,0,0
The spots of the numbers decide how many of each group you fight. (6 meaning you will fight 6 order = 1 chars, the first 1 means you will fight 1 order = 2 char, the last 1 means you will fight one order = 3 char)
