With two mics, take one mic in each hand. Freestyle with both, taking turns on each mic. You can use a different vocal style or persona in each mic. You can do a fake back-and-forth duet or conversation with yourself. Try adding live effects to one of the mics, like echo or like autotune. If you don’t have a mic, you can get the effect by freestyling while alternately turning to your right and left side, or switch between two different body postures.
Switching mics helps to switch your style by physically embodying the changeover. It can help you do faster style switching, and remember to switch it up without getting mentally carried away by your freestyle drift.