Also known as: ゲッソー, gesso, bloober
Bloopers (often referred to as Bloobers until Paper Mario (Series), though Blooper was in use beforehand) are squid-like creatures that are found in the Mario series. They made their first appearance in Super Mario Bros. 1, and various kinds of them have appeared in most Mario games since, normally as enemies.
Their Japanese name is ゲッソー (Gessoo) which is a pun on げそ (geso; squid legs) and officially romanized as "Gesso".