Their attack consists of getting close to either Bro. and trying to slam them, but can be avoided if either Bro. uses their Hammer and they may hide in their trash cans when being approached by being attacked and therefore Mario and Luigi must quickly attack the Junker Can before it attacks them. Junker may eventually grab Luigi with its suckers and throw him into one of the Junker Cans and therefore he must be rescued by Mario with him having to defeat the Junker Can before it defeats Luigi. After defeating a Junker Can, a Fishbone, Chain Chomp, or a Nooz will go after Mario or Luigi, depending on who defeated the Junker Can.
When Mario is defeated while Luigi is still in a Junker Can, Luigi will have all of his HP drained.