Which of these champs is good against Ultron in 5.4.6

Four rounds to reach this Boss.

Thinking Rintrah (need to rank up) but needs to practise. Any other champs suggestion and if Rintrah works ?
Edit: Have a 4-Star Venom not in image.
Thanks.

Thinking Rintrah (need to rank up) but needs to practise. Any other champs suggestion and if Rintrah works ?
Edit: Have a 4-Star Venom not in image.
Thanks.
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Put on boosts, bought one 500 units Potion and Revive Bundle and fought a war of Attrition and finally KO Ultron.
From the 5-Star Nexus, obtained Human Torch 😁 and Kushala from 5-Star Hero Crystal.
Gave up the idea of using Rintrah. Would still give it a try sometime in the future (maybe 🤔 ).