Watching the videos, it all looks like a single shot -- no cuts. Likewise, from the way the camera is handled, it looks as though they *are* shot on cell phones. We have two potential explanations, that I can see:
1) It's a hoax.
2) We have physical entities that resemble (or perhaps are) germanic-style gnomes.
In terms of the potential for a hoax, the following has been brought up:
Film in HD, edit, degrade image, compress as shit, upload to Youtube.
It doesn't seem to me that that's particularly likely, unless it was filmed in HD on a *very* small camera. Likewise, shadows and such look alright.
In terms of a hoax with actual props (say, a remote control device of some kind, or -- as Micah of the gralien report suggests -- an actual small or deformed person), the fact that it's a single shot makes this far less likely. Anyone who has filmed and edited videos can tell you how difficult it is to manage without cuts, and anyone who hasn't must only look to Hitchcock's "Rope" to see precisely how well a master director manages it.
The second possibility is that something (which appears to be a gnome) is hanging around Argentina and showing up on cameras. There is, of course, difficulty in using this when you subscribe to any variant of the psychological explanation for fortean phenomena (particularly gnomes and other fae-folk), except perhaps pareidoelia. However, I am hard pressed to think of what else, aside from a gnome, this looks like.
Altogether, these videos appear to pose a problem for everyone who doesn't believe that actual gnomes exist in Argentina.
If anyone has any ideas for other methods by which a hoax like this could be perpetrated, other things that the 'gnome' could be in the video, or other hypotheses for how entities of the non-physical variety could show up on film, please comment and let me know.