The Mutant Skeleton (MCPE) is a mob that can only be obtained through mods. It does not look exactly like normal PC Mutant Skeleton, as it has different body and different attacks.
Mutant skeleton attacks at the player with its bow that holds on its hand. It also has a smaller bow on its right leg, but it does not use it. When killed, 3 normal Skeletons spawn and attack the player.
A bow is recommended for this battle, while a diamond sword is good too. Armor is also recommended, while potions of healing/harming would make the fight easier.