After being attacked, the Mimic will levitate itself and will start to spawn Mini Sliders, which are small, red sliders. The Mini Sliders will home-in on the player and attack them, dealing three hearts of damage each. Going too far away will make Mini Sliders despawn and cause the Mimic to go dormant.
An easy way to kill a Mimic is to lure them inside a narrow corridor and build a wall of blocks on your back, therefore negating the knockback effects of the Mini Sliders. Keep hitting them and use Healing Stones if you ever have the need to and this boss can be taken down with ease.
Issues relating to Slider Host Mimic mob are maintained on the bug tracker. Report issues for Slider Host Mimic there.