Dutches, dreng or mordacai(hp burn booked), coldheart, royal guard, Mm should work for spider.

I'm not sure if I would add Royal Guard to the team. His attack may kill the Spiderlings, so they don't burn anymore. Armiger should be better for Spider 20.

The UNM 100 million can be bought in the shop. It's not 100 million in one fight (only a few players would have Arbiter if that would be the case), but per day. You can buy extra keys for 100 gems. As long as you have a team that can deal 10 million per fight... 4 free keys a day --> 600 gems to get Arbiter.

I think Duchess, Kreela, Grush, Giscard and Mighty Mouse could be a team. Giscard needs to be levelled before he can join, of course.

;-) Mighty Mouse is stil Fayne in my imagination...I refer to him as Rat King...

Thanks all.  Had thought about a similar team with Drexthar instead of Mordecai.  But maybe it is time to bring Mordecai to 60.  

Drexthar works totally fine. The fight may take a few seconds longer, as the Spiderlings don't have burn in their first turn, but it definetly works for Spider 20.