Warriors Who Could Defeat Arjuna Without Krishna’s Help: A Mythological Analysis

there were some characters who can defeat Arjuna in battle alone and then Krishna would have to save him. However I would exclude Rama from this list because although Lord Rama is superior to Arjuna he and Krishna both are same. And since the question has Krishna along with Arjuna then there is no point adding Rama because they both are same

Parshurama

He was the sixth incarnation of Vishnu and the strongest warrior of Treta yug after Shri Rama. He defeated and killed the mighty king Kartavirya Arjuna, obtained almost every celestial weapon from Mahadeva and his most amazing feat was to fight a battle with Mahadeva for 21 days and overpower him according to the puranas. Same Arjuna failed to defeat Mahadeva in battle in a single day.

Hanuman

He was the incarnation of Lord Shiva and son of Vayu dev. He was blessed with unlimited powers from gods. He was given a boon that no one can kill him with the use of celestial weapon. He had the ability to change his form and size and could fly across the sky. He had lept across 1000 yojana sea to find Sita. Arjuna did not possess the powers Hanuman had with him. His celestial weapons like Pashuatastra will have no effect on Hanuman and ultimately he will be defeated.

I would also include Sage Vishwamitra and Sage Vashishta. I would call them powerful than Arjuna but only because of their knowledge of celestial weapons was higher than Savyasachi

Sage Vashishta had Brahmandastra the most powerful weapon of the universe by which he destroyed all the celestial weapons of Vishwamitra including the Trident and Sudharsana discus. He can counter all the celestial weapons of Arjuna with his powerful weapon.

On the other hand talking about Sage Vishwamitra there was nothing he did not know about warfare. He possessed all the celestial weapons of Treta yug including Pashupatastra, Vaishnavastra, Narayanastra, Brahmashirastra, Trishul and Sudharsana chakra too. If he uses those powerful weapons then he can one shot or even kill Arjuna if Krishna is not helping him.

However if it is a battle of plain archery then I do not think Sage Vishwamitra or Sage Vashishta can defeat Arjuna even if he is without Krishna. In normal archery or in battle of normal celestial weapons like Agneyastra or Roudrastra Arjuna can defeat them both. then the battle of Arjuna with Sage Vishwamitra or Sage Vashishta would be just like the battle of Bhishma and Parshurama

And I am saying this in context of Shiva dhanurveda made by Ved Vyasa who said that Arjuna was the greatest archer after Rama and Mahadeva.