Anyone who comes into contact with the ultrasonic waves emitted by a courting male experiences a positive mood shift.
(From Bulbapedia) Swoobat is a blue, bat-like Pokémon. It has fused, pointed ears with striated, lighter colored insides and a pink, heart-shaped snout with a single nostril. Swoobat's nose can produce many different ultrasonic waves. When it shakes its tail vigorously, it is producing sound waves powerful enough to destroy concrete. In contrast, it produces waves during courtship that can gladden any who hear it. Two wide, rounded teeth are visible in its lower jaw. A mane of shaggy, light blue fur surrounds its neck. Its black wings have a claw at the joint, and its small black feet have three toes each. It has a bare, pink tail that is twisted with two short prongs at the tip. In the anime, it is seen to hang from this tail rather than its feet as it sleeps.
(From Bulbapedia) Swoobat appears to based on a flying fox and a heart-nosed bat.
(From Bulbapedia) Swoobat may be a combination of swoon or swoop and bat. Its English name containing the English name of its pre-evolved form (Woobat) mirrors how its Japanese name (Kokoromori) contains the Japanese name of its pre-evolved form (Koromori).