Karna is one of complex characters of Mahabharata. First he is seen coming and making fun of Arjuna at the Tournament of Kuru princes. When Bhima finds out that Karna is son of charioteer. Bhima insults him. But Karna hates Arjuna instead of Bhima. Then Duryodhana makes him King of Anga knowing that Karna is equivalent to Arjuna. Karna is always jealous of the fame and archery skills of Arjuna.
Karna joins Duryodhana and Sakuni in plotting against the pandavas. First Karna, sakuni, duryodhana join hands to kill pandavas in wax house.
Next Karna meets Arjuna disguised as brahmin at draupadi's swayamvar. He fights with Arjuna disguised and finds it unable to defeat Arjuna so he gives up the fighting. When it is later revealed that the disguised brahmin was Arjuna. Karna hates Arjuna more.
Next Karna insults draupadi by calling her a whore. It is Karna who instigates Dussasana to strip Draupadi of her clothes. Then Bhima vows to tear the chest of Dussasana and drink his blood.
Karna instigates duryodhana to make fun of pandavas when they are living in forest. They try to mock pandavas but they themselves are defeated by gandarvas. Karna runs away from battlefield leaving Duryodhana to gandarvas.
As i have read in some blogs these days because of TV serials and movies. The great Pandavas are considered as cowards. Evil souls like Duryodhana and Karna are considered as great men. Bhima is shown as a fat, greedy and short tempered warrior.
But Bhima is not as such. Bhima is the second hero of Mahabharata after Arjuna. He is extremely strong and is not afraid of anyone. He defeated Karna many times during Mahabharata war and forced him to retreat chariot less. Karna once defeated Bhima by hiding in his chariot. Bhima was weaponless at that time. Bhima then challenged Karna to a wrestling duel. But Karna got afraid and declined the challenge and went away.
On 17th day of Mahabharata warKarna insulted Yudhistira. Then Bhima vowed to kill Karna.Bhima fought with Karna and made him unconscious. He was about to cut of the tongue of Karna but Shalya stopped him and told him Arjuna has vowed to kill Karna so leave him. Thus Bhima spared Karna. In TV serials they did not show this scene. This is available in Mahabharata translation by Kisan Mohan Ganguli.
Comparing Bhima and Duryodhana. Bhima was much stronger than Duryodhana but Duryodhana has more skill in mace than Bhima. Bhima is the protector of remaining pandavas including Arjuna during burning of wax house.
After mahabharatha war. Yudhistir performed aswamedha yaga. The sacrificial horse is to roam freely and anyone who captures it will be considered enemy of yudhistira and Arjuna had to defeat him. The horse goes to manipur. Babruvahana, the son of Arjuna and chitrangada and prince of manipur knowing that his father comes to receive him with due honours. But Arjuna gets angry and tells him "i came as a representative of Yudhistir. I am your enemy not your friend you should fight me".
Arjuna rebuked his son in bitter words. Ulupi amother wife of Arjuna and stepmother to Babruvahana comes to babruvahana and tells him to fight his father. Babruvahana fights with Arjuna. Both fight fiercely. Babruvahana shoots an arrow that kills Arjuna. Later babruvahana faints. Chitrangada comes to know that her husband is killed and her son is wounded. Chitrangada comes to battlefield and grieves Arjuna's death. Chitrangada blames Ulupi for making Babruvahana fight with Arjuna
Babruvahana regains consciousness and knowing that he killed his father prepares to commit suicide. But Ulupi comes and stops him and tells him "this is an illusion created by me, Arjuna cannot be defeated by Indra himself. Arjuna's death was caused by the curse of vasus as Arjuna has killed his grandfather Bhishma in unjust way"
Ulupi then revives Arjuna with gem that can revive dead people. Arjuna wakes up and is happy to see both Ulupi and Chitrangada and Ulupi explains about the cause for his death. Arjuna is happy with what Ulupi did. Babruvahana asks Arjuna to come to his palace but Arjuna says he has to go and takes leave of Ulupi, chitrangada and Babruvahana
Why Arjuna sould not encounter Nagasthra is not that Arjuna did not have powerful asthra to counter it.
Actually he did not know that it was nagasthra as Karna himself did not know that snake aswasen entered the arrow. Aswasens mother was killed by Arjuna during the burning of Khandava forest. So he entered Karna's arrow to take revenge.So it was not the greatness of karna or inferiority of Arjuna here. Telugu and tamil movies have shown as if karna had nagasthra or something which is not true.