After the mythbusting of Karna,this will be a general myth busting thread for Mahbharata. Questions and suggestions are welcome, I will try to answer them as best of my knowledge. I will be citing mainly BORI edition, KMG edition and Gita Press Edition of Mahabharat. #Mahabharat

Myth 1: Hanuman was present on Arjuna's banner and protected Arjuna.
Truth: The chariot and banner were given to Arjuna by Varuna and the ape on banner was created by Vishwakarma.

Myth 2: Gandhari made Duryodhan's body like vajra
Truth: This is false and never occurs in Mahabharata. When Gandhari looks at Yudhisthir, it is the first time she looked at something since she bandaged her eyes.

Truth: Duryodhan's upper body was already made like vajra by daityas in Ghosa Yatra Parva.

Myth: Sahdeva knew everything in future after eating a portion of Pandu's body/Pandu's brain
Truth: No such ability is mentioned in Mahabharat and Pandu was cremated immediately with no mention of such acts.

Myth: Suta were of lower caste and could not hold royal stations.
Truth: Already covered but here is some more proof.
1. Anga King Vijaya was a suta
2. Sudeshna-queen of Matsya was a suta as well a Kichaka-commander of armies

Myth: Shakuni was limp in Mahabharata and wanted to destroy Kuru dynasty
Truth: Shakuni was never limp, was happy with the marriage of Gandhari, it happened as Gufi Paintal gave a demo of the character as such, he even asked Duryodhan to let go of his jealousy towards Pandavas

Myth: Mahabharata has no protagonist/antagonist, it is just a tale of good vs bad
Truth: Adi Parva makes it clear who are the villains and who are the heroes (Hint: Karna is a villain)

Now a bombshell. Please don't kill me Radhe Krishna fans
Myth: Radha is present in Mahbharata
Truth: There is no mention of Radha in Mahabharata or Vedas. She is first mentioned in Srimad-Bhagavatam

Myth: Karna was a "daanveer" and never denied anyone
Truth: Karna made a vow of charity only in Vana Parva and it was only for Brahmins. As already covered, he refused to give them to Indra if he does not give him a boon. Additionally "daanveer" word never occurs in Mahabharat