I used Tholin on Zem. I had to retry 2 games against aw Dokras because of Tholin feeding his ult, but I used even less time to complete CoF. Nice suggestion!
Tomorrow I'll try Gizmo again
The reason zem is never a problem is because you have taurus and tholin ult to knock zem back into the team if the enemy has a 7 star zem or something. You can start off with taurus and jasmine ult then use tholin to knock zem and any other frontline heroes back even more so they become stacked for a massive sera ultimate. Finish it off by using zem to tear through any surviving units to complete the stage.
Alternatively I've actually used leah instead of tholin for a 0 tank team since jasmine heals my taurus enough not to mention he often takes 0 dmg. Also possible to replace gizmo with leah if there are a lot of really high magic res heroes on your server like vincent namtar ect... I just don't like using zem cause his ultimate takes so long to cast and he usually does no dmg at all. Tholin gives haste, recovers energy even faster with taurus and does great aoe to the whole team with his weapon toss, ultimate is also great for stacking enemies for taurus and serafine ults.
If you are not a top player on the server I feel like the physical team will do much better for you but I consider nightshade to be an absolute must in thay set up since ns and leah do like 80% of the dmg on the team.