From Jatland Wiki

Ashwasena (अश्‍वसेन) was son of Naga Takshaka, whose mother Arjuna had slain. He was saved by Indra, while Khandavavana was put into flame by Pandavas. Five mighty arrows shot by Karna.

A little known story is that at the time of the great war when Arjuna and Karna come face to face with each other, the Naga King Ashwasena desirous of avenging the death of his mother from Arjuna, in that battle quietly slips into the quiver of Karna in the guise of an Arrow. It is this Arrow that had almost killed Arjuna had it not been for Krishna who by pressing his feet on the chariot sank it one cubit deep into the earth hence the arrow missing its aim.