Grolem 13 appears in Rayman 2: Revolution only. Grolem 13 is the guardian of the fourth mask of Polokus. The player fights him in the Iron Mountains level. Grolem 13 is more like Axel than Foutch, but still has the same appearance as Axel and Foutch, only much more bigger and harder than them. It would seem that 'Grolem' is his species, and if so, that makes Axel and Foutch also Grolems. The number 13 also suggests there were several Grolems created by Polokus.
For an unknown reason, there was no Guardian for the fourth and final mask in the Playstation 2 version of Rayman 2. It is unknown what happened to last Guardian, but some theorise that the Guardian was there but died, or he simply buried the mask and abandoned his duty and dissappeared.