Waddle Doos are a projectile thrown (rarely) in King Dedede's Smash B attack, Waddle Dee Toss. Unlike the Waddle Dee, it appears to be able to attack with it's beam attack as it remains on the field.
In Kirby games, Kirby obtains Beam ability when he swallows a Waddle Doo.
Trophy Description
A creature identified by a single, unblinking eye. Like Waddle Dees, Waddle Doos roam about Dream Land and sometimes use parasols. Unlike their counterparts, though, they hate being approached--they'll fire a beam of energy at anyone who nears them, so don't think they're harmless like Waddle Dees. If Kirby swallows one, he copies the Beam ability and gains a jester's hat.
- Kirby's Dream Land, 1992