B.G. 2.2 : Killing of Pralambasura

One day while Krishna and Balarama were engaged in playing with their cowherd boyfriends in the forest, a very dangerous demon named Pralambasura came in disguise of a little innocent cowherd boy and joined the company of Krishna's friends. He was just doing all the activities like his other friends, herding the cows, playing and jumping and throwing balls, jumping like frogs and everything like that and singing and playing flute and buffalo horn. But Krishna knew within his heart that this was a demon that has come to kill us. But Krishna pretended that he did not know. Instead of attacking him, he welcomed Pralambasura  into their game.

Krishna decided to form two teams, one led by him, the other by Balarama. He would invite a member from each team to fight a duel. Afterwards the winners would be rewarded with a ride on the loser's back. Pralambasura took Krishna's side, but Krishna decided to purposefully lose the game. Meanwhile, Pralambasura, thinking  Balarama to be weak, decided to carry him on his shoulders. He carried him far into the jungles and there changed into an enormous giant who nearly touched the skies. Balarama, seeing Pralambasura's changing form, also grew in size. Like a mountain, he rose up on the demon's back and struck his neck. Pralambasura died on the spot.

Pralambasura represents impure desires disguised in the dress of good desires in order to take us away from path of dharma or the company of Krishna.  But however nicely dressed they may be they can't escape from the sight of Krishna or His pure devotee. 

       B.G- 2.2
kutas tvā kaśmalam idaṁ
viṣame samupasthitam
anārya-juṣṭam asvargyam
akīrti-karam arjuna  
 

Translation : The Supreme Personality of Godhead said: My dear Arjuna, how have these impurities come upon you? They are not at all befitting a man who knows the value of life. They lead not to higher planets but to infamy.

Arjuna wanted to give up the battle on the grounds of his magnanimous attitude for the most respectable Bhīṣma and his relatives, but Kṛṣṇa considered that sort of magnanimity mere weakness of heart.

Here demon of weakness of heart disguised itself as quality of Magnanimity of heart and Arjuna was considering it as his dear friend.

References

1. http://www.radhanathswami.net/vrindavan-yatra/04-56-the-killing-of-pralambasura-lecture-by-radhanath-swami-2/

2. http://www.vedabase.com/en/bg/2/3

3. http://www.kidsgen.com/fables_and_fairytales/indian_mythology_stories/balarama_and_pralambasura.htm