Koga's Golbat is one of Koga's Pokemon. Out of all of Koga's Pokemon, this is the one he uses the most.
Koga used Golbat's ability to watch and controll Arbok from a distance whle it was fighting Blue's Charmeeon inside Pokemon Tower.As a result, Koga didn't see that Blue used a dead Psyduck's corpse to prevent Arbok's acid attack from hitting Charmeleon.
Later, Golbat was used by Blue in order to find Prof. Oak who had been abducted by Rocket and locked up in the Silph Co. building.
It was returned to Koga during Koga's and Blue's battle aginst Agatha.