From the Super Mario Wiki
Retrieved from "https://www.mariowiki.com/index.php?title=Frame_Boo&oldid=2706067"
Frame Boos are Boos made out of a metal frame and only appear in level 6-5 in Yoshi's Woolly World and Poochy & Yoshi's Woolly World. If Yoshi hits them with a Yarn Ball while they are chasing him (i.e. while Yoshi's back is turned), they will turn into Boo-like balloons and rise temporarily, before they break free and return to their original form. Yoshi can also return them to normal Frame Boos by untying the ribbon at the top of the balloons with his tongue.
A Frame Boo resembles a normal Boo, but has a frame around a glowing core. Furthermore, when Yoshi looks towards a Frame Boo, the glowing core turns red, and whilst chasing Yoshi they have a blue glow.
Names in other languages