Meca-Penguins are little toys shaped like a penguin, that walk for a little while and then explode, inflicting a lot of damage. Twinsen can hold only one Meca-Penguin at a time. In LBA2, there seems to be an upgraded version of them, the Nitro-Meca-Penguins.
Meca-Penguins are most useful angainst red clones, as they will chase them and hit them until they both explode together.
"Meca-Penguin. Red clones just hate this stupid toy."