Custom Bosses Not Spawning ?

Ok so I put my bosses in my randomspawns (Bob,Slenderman.) I only put 2 and they don't work. But, the SkeletonKing and SkeletalKnight work, but I didn't make them because they were already there. But mine don't work, please help, here's my config where I put them.

RandomBob:
Mobtype: Bob
Worlds: world
Chance: 0.6
Priority: 1
Action: add
RandomSlenderman:
Mobtype: Slenderman
Worlds: world
Chance: 0.6
Priority: 1
Action: add
Conditions:
- outside true
- night true