I've only seen one tiny enemy so far, it was a huge gator level 14, but it had shrunk down to the size of a swamp gator. My friend has seen smaller enemies, but i'm still searching
As for the jumping around and slipping underground, i didn't bother to fight it to find out lol. At least with the amount of issues now on open as well as test due to the early bugged release, they should be quicker to fix them (i hope).