May want to look at auto-battles AI.

Just watched my champs against Tower Boss (spider), & through at least 12 rounds, they never used primary AoE attacks. 

Kael never used Acid Rain.

Elven Huntsman never used Slaughter Volley.

Miscreated Monster never used Lightning Storm.

Scyl never used Wing Buffet.

As a result, they were being beaten by the Boss & it's minions because the minions were never taken out, & so were able to simply continue to pile on the poison markers.