https://imgur.com/oMQSwpL

I beat SL10 with this lineup that is a little different than what I have seen other do. My Oberon dies instantly and i think his 1 attack didn't make a difference. I'm pretty sure this works with no Oberons. The HWs are just for some dmg boost, they all die 1st round.

My little Idle Heroes secret I've always felt is 6* Rosa. I used him to shoot up to an inflated Tower lvl back before E5 meta as well. Whats so great about Rosa 6* is that he gets 12% dmg reduce for the whole team for 3 rounds and his auto or active (with energy arti) debuffs. He is THE best suicide support at 6* in the game. I can't emphasis how good the 3 turn dmg reduce is for sub-15 round PvE challenges like SL, tower, and raid.

Strategy: The important part to using Rosa is giving him just the right amount of HP with gear/stone to survive a single attack, but still drop below 50% (1 shots dont give the buff). Then just attempt over and over until Valk carries you. I dont know if Valk hp% dmg works with HW debuff, but random lvl 100s that are useful are oberon, groo, and HW. Probably the ultimate (cheap) setup is 6* Rosa with energy arti, 3 lvl 100 Oberons, HW with energy arti (attack reduce).

Good luck! Im hope this helps others like me that invested everything into Valk and thought i was screwed because i didnt have 5 Oberons or a 10* Groo.

Edit: Forgot to mention, my Valk is maxed with 1 3 1 1 2 enable choices. Took me 2 days of attempts I think? May even have been less, but I can't remember. Its just about a little luck with the boss jot using his active 1st round too kill Rosa. And then hoping your E5 passive (unbending will) doesn't get proc'd before you get healed by dear. You live much longer that way.