Act 5.4.6 has Classic Ultron (OG Ultron) boss to fight. What makes this fight different is aggressive regeneration, power gain, and other buffs. Every time one buff will show up there, but it will not get activated unless you put a debuff on Ultron. Even if you use parry, that buff will activate. If it is a power gain buff, you are likely to get killed as Ultron will get Level 3 Special bar filled.
What are the Best Champs to use against Act 5.4.6 Boss Classic Ultron
Loki: Loki’s Curse and Buff steal is the key to winning. Try getting L3 filled and use it to set a curse on Ultron. Loki will steam all buffs as long as Ultron is under the curse. You can use a Heavy attack to reset the curse timer: Just Parry and use Heavy. Once Loki Steals the Fury Buff, he will hit like Ultron and kill him quicker than any other champ.
Medusa: Medusa armor shatter will help you win. Once the Ultron’s Armor is shattered, his regeneration and Power gain will stop, and he will take more damage.
Star-Lord: Just don’t lose the combo and Ultron will be dead very fast. SL must be duped, though.
Void: Spam L1 to reverse Regeneration to Degeneration and it will also help you to stop the Power gain. After Loki, Void is the best counter for the fastest killing.
Nebula: Get 5 charges and then Ultron will not gain any buff. She will reduce its ability accuracy by 100%. However, you will have to intercept. If you parry Ultron, make sure you get those 5 charges first before you intercept again.
Vision Arkus: He can break armor, apply cold snap and shatter armor with Special 2. After the armor is shattered, Ultron will not gain any power (not even from attack). Coldsnap will also disable its evade.
Doctor Doom: He can steal power and a duped Doctor doom can also steam power gain. He can also apply a stagger to nullify the next debuff and can nullify buffs with Special 1.
Iceman: Iceman is immune to bleed and poison, so if a slip-up happens, it will not kill him. Iceman starts a fight with Cold Snap and you can again set a cold snap with L1 or L3. Ultron cannot evade under the effect of Cold Snap that will make him easier to fight. However, this fight will take a little longer.
Scarlet Witch: Scarlet Witch has various abilities, like Nullify, Power Lock, Power Gain, etc. Her L2 does a ton of damage. I have seen almost 50K Damage with her L2. So she makes it very easy to fight as long as you don’t get hit.
Quake: Quake is also great if you know how to play her. She can kill Ultron without a hit.