i am guessing you have multiple combos that will work. 

tayrel apo mm rg ch maybe?

My Spider 20 team:

Apothecary, Scyl of the Drakes, Miscreated Monster, Royal Guard, Coldheart

Gets the job done quick is consistently wins on auto runs

You probably don't need the off affinity tank, but kantra is perfect for this role. But as I said, your roster appears like you have multiple options to flat out nuke spider20 with mm shield providing plenty of 

2 Coldheart, Royal Guard, Kymar and Serris

Potential below 30 seconds team

The set up JoinMe recommended with Kymar could work.

You just have to build your Coldhearts with 100 more Speed vs. Kymar.

You would need your Coldhearts to move 2 times before Kymar has a turn.

2 Coldhearts, Royal Guard, Miscreated Monster and Serris

Its another set up you can do which should win in around 1 min.

The set up I am recommending doesn't reset skills.

It just uses M.M Big Shield to stall the fight till the Coldhearts skills come off Cool Down.

You will do 3 nukes.

Put Big Shield + Survive few hits.

Than cycle back to do another 3 nukes.

Just make sure your Serris has lower HP vs. your Coldhearts so the Baby Spiders target Serris.