The emblem of Hanuman on the flag of Arjuna is another sign of victory because Hanuman cooperated with Lord Rama in the battle between Rama and Ravana, and Lord Rama emerged victorious.
Krishna as saarthi in mahabharata
Krishna as saarthi where as Hanuman on Flag in mahabharata
Lord Krishna is Rama Himself, and wherever Lord Rama is, His eternal servitor Hanuman and His eternal consort Sita, the goddess of fortune, are present.
Therefore, Arjuna had no cause to fear any enemies whatsoever. And above all, the Lord of the senses, Lord Krishna, was personally present to give him direction. Thus, all good counsel was available to Arjuna in the matter of executing the battle. In such auspicious conditions, arranged by the Lord for His eternal devotee, lay the signs of assured victory.
Hanuman, decorating the chariot’s flag, was ready to shout his war cries to help Bhima terrify the enemy. Earlier, the Mahabharata had described a meeting between Hanuman and Bhima.
Once, while Arjuna was seeking celestial weapons, the remaining Pandavas wandered to Badarikashrama, high in the Himalayas. Suddenly, the alakananda River carried to Draupadi a beautiful and fragrant thousand-petaled lotus flower. Draupadi was captivated by its beauty and scent. “Bhima, this lotus flower is so beautiful. I should offer it to Yudhisthhira Maharaja. Could you get me a few more? We could take some back to our hermitage in Kamyaka.”
Bhima grabbed his club and charged up the hill where no mortals were permitted. As he ran, he bellowed and frightened elephants and lions. He uprooted trees as he pushed them aside. Not caring for the ferocious beasts of the jungle, he climbed a steep mountain until his progress was blocked by a huge monkey lying across the path.
“Why are you making so much noise and scaring all the animals?” the monkey said. “Just sit down and eat some fruit.”
“Move aside,” ordered Bhima, for etiquette forbade him to step over the monkey.
The monkey’s reply?
“I am too old to move. Jump over me.”
Bhima, becoming angry, repeated his order, but the monkey, again pleading the weakness of old age, requested Bhima to simply move his tail aside.
Proud of his immense strength, Bhima thought to pull the monkey out of the way by its tail. But, to his amazement, he could not move it in the least, though he exerted all his strength. In shame, he bent down his head and politely asked the monkey who he was. The monkey revealed his identity as Hanuman, his brother and told him that he stopped him to prevent him from the dangers and rakshasas in the forest.
Transported with delight, Bhima requested Hanuman to show him the form in which he crossed the ocean. Hanuman smiled and began to increase his size to the extent Bhima realized he had grown beyond the size of the mountain. Bhima bowed before him and told him that inspired with his strength, he was sure to conquer his enemies.
Hanuman gave parting blessing to his brother: “While you roar like a lion in the battlefield, my voice shall join yours and strike terror into the heart of your enemies. I shall be present on the flag of the chariot of your brother Arjuna. You will be victorious.”
He then offered Bhima the following blessings.
“I shall remain present on the flag of your brother Arjuna. When you roar like a lion on the battlefield, my voice will join with yours to strike terror into the hearts of your enemies. You will be victorious and regain your kingdom.”