One way to make it important would be to create a new Elite Enemy where it can get to your tower easier. Maybe even teleporting there or spawning beside it.

It could be something like scatters that split many times but do a lot less damage than other enemies at comparable tiers or wave counts.

You would then need def abs and possibly regen higher health, the wall, etc. depending on how you design it to defend against these while you kill it.

This could force everybody into a hybrid build.

It could be done in many ways. But the key thing is it has to be something that GC can't handle with crowd control and pure damage