why were the muttation?

I believe you're asking about the monkeys; if not follow the source link below.

In the 75th Hunger Games, the third Quarter Quell, one section of the arena, which was a clock, contained a mutated species of an orange colored monkey that viciously attacked the tributes, harming them and even killing the female Morphling when she saved Peeta's life. They used their paws and their teeth to make deep punctures in their victims' flesh that looked harmless, but in reality were deep enough to cause internal bleeding. The group left the beach after the morphling died so the hovercraft could take her body away.