[Minecraft Commands] Naturally Spawning Custom Mobs

Custom Mob Command
/summon <Mob> ~ ~ ~ {DropChances:[1.0f,1.0f,1.0f,1.0f,1.0f],Equipment:[{id:<hand>},{id:<feet>},{id:<legs>},{id:<torso>},{id:<head>}]}

Finding A Host Mob (Can Be Any Mob and Radius)
/execute @a ~ ~ ~ /testfor @e[type=Zombie,r=25]

/execute @a ~ ~ ~ /scoreboard players set @e[type=Zombie,r=25] Rare 1

Summon Custom Mob
/execute @e[score_Rare_min=1] ~ ~ ~ /summon Skeleton ~ ~ ~ {DropChances:[1.0f,1.0f,1.0f,1.0f,1.0f],Equipment:[{id:258,Count:1},{id:301},{id:0},{id:0},{id:0}]}

Kill Host Mob (Despawn In Void)
/tp @e[score_Rare_min=1] ~ -200 ~

Reset Scoreboard
/scoreboard players reset * Rare

(Last optional command that was not shown in video. Sorry.)
Re-Summon Host Mob
/execute @e[score_Rare_min=1] ~ ~ ~ /summon Zombie ~ ~ ~