A really common Misconception about Bhisma is that He alone fought Lord Prashuram, Which is false. In reality He was being protected by Godess Ganga, Otherwise he wouldn’t have survived the clash.
He then beheld his mother Ganga, that foremost of the rivers, stationed on his car. Indeed, it was that great river-goddess who had controlled Bhishma’s steeds in the combat (after his charioteer's fall)! Worshipping then the feet of his mother and of the spirits of his ancestors, Bhishma ascended his car. His mother then protected his car, steeds, and all the implements of battle.
Coming to Karna, People have a Misconception about him that He can't shoot Arrows from the both the Hands and low ball him. However, The epic says otherwise.
"While employed with his hands in taking up an arrow, fixing it on the bow-string, stretching the string and letting it off, none could notice any interval between those acts. And while Karna was thus engaged in shooting his arrows right and left, his bow incessantly drawn to a circle, like a terrible circle of fire. The keen pointed arrows, equipped with wings of gold, shot from Karna's bow, covered, O king, all the points of the compass, darkening the very light of the sun.
Karna is effectively ambidextrous as described in the Epic. Majority of the people think that only Arjuna is ambidextrous cause it is one of his permanent epithet is wrong.
My Answer is based on Mahabharat epic and refers to authentic versions including
- English translation by Kisari Mohan Ganguli (KMG)
- Neelkanth edition Sanskrit Hindi version of Gita Press