Mirio can just attack his ice side, also Todoroki can't move while using both powers at the same time so Mirio can just wait until he movesMiro has to breathe sometime since he cant while phased (episode detailed how air even passes through his lungs, and light passes his eyes, and and sound through his ears, so he cant breathe, see, or hear) I could imagine a situation in which todo could have the entire area ablaze or ice continually flowing that would essentially immobilize or keep mirio at bay. Fire would also make it impossible for mirio to breathe, though todo would have to take precautions for the ground under him.
Worst case scenario for Mirio it is a stalemate
The only ones that are popular, the other ones are as popular as Iida and Momo for exampleDeku x Bakugo
Deku x Todoroki
Deku x Iida
Deku x Mirio
Deku x Uraraka
Deku x Momo
Deku x Asui
Deku x Mei
Deku x Toga
Deku x Mina
Deku x Bakugo's Mom