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You didn't say which archdemon is this one , so I'll assume he is like the last one ( huge damage stun targets )
And my answer is:
Hero talent Crests pets
Pumpkin Duke Regenerate Psyshield Yulephant
Beast Tamer Slow down Empower Little Havoc
Druid Slow down Empower Ckickaboom
Cupid Slow down Empower Glacie
Trixie Treat Slow down Empower Aviar
Siren Slow down Empower Finix
That's for heros/ talent/ crests/ pets. The next part of answer is why . My heros are the same except for Pumpkin Duke Regenerate/ Psyshield/ Yulephant
This talent Will give pd the energy / healing to proc faster and live longer. Psyshield will give him immune to stun . I choose Yulephant pet on him because i will drop him nearest the archdemon and Yulephant skill will trigger when pd attacked.
The rest of my heros are the same. Slow down for more damage ( when slow down triggered it deal 100% damage) . Empower crests it will give them the energy event when thay stunned always ready to proc. Also I choose damage pets because that's what I need them to do.
About the heros i used
Pumpkin Duke Druid Cupid for buffs my heros
Siren because her skill ( increase dmg) same as Ckickaboom and Beast Tamer
Beast Tamer because his skill ( increase dmg) also he is a good dps hero
Trixie Treat because she is a great dps hero.
For dropping heros.
Start with Siren then the rest of the heros except for Pumpkin Duke. After that drop Pumpkin Duke nearest the archdemon to make sure the archdemon attack Pumpkin Duke first.
I guess thats all.