It starts by firing bursts at the ground in random spots, then doing the same against the ceiling. After it does these attacks, it will angrily fire a barrage of shots all over the ground area. It will then repeat it's chain of attacks.
There is a hover booster that can be used to access a rail above the Mutant Iris for attacking it.
While playing as Milla, she can find ride Sparky, which is similar to Mutant Iris hence it's attacks and behaviour and use it for the rest of the level to beat tough enemies, until the fight against the Shade Beast. Sparky looks similar to a Mutant Iris, but with a green and orange color scheme, and an eye similar to Milla's. Shooting up with the Iris while moving will damage Milla.