Eye-eating horse-sized aberrations, lifted straight from Aztec myth.

To start off, 7 HD are bad. The somewhat high bonus to strength (+10) and assorted bonuses to most other stats are neat. 40 ft. swim speed is great, but 20 ft. land speed would be embarrassing on a medium creature, let alone a large one. Natural weapons are okay: a secondary 2d6 bite and a 1d6, 10 ft. reach, 'tail hand'.

Ahuizotls of course have a number of quirky special abilities. Mimicry lets them mimic voices using Bluff (have you considered a wand of ghost sound), Improved Grab does its usual thing (with the added caveat of only working on medium-and-smaller creatures), Drowning is hilariously redundant (if you can grapple something for 2+ minutes, it's probably dead at the end anyways).

Finally, there's a signature ability of sorts in Blinding Strike, which makes all tail hand and bite critical hits permanently blind the opponent. I suppose it's neat, and some specialized critfisher could probably exploit it decently well, but at the end of the day you're just occasionally copying a mediocre 2nd-level spell.

Anyway: while the ahuizotl has some neat quirks, its overall chassis is mediocre and its special abilities are not powerful enough to make it shine. -0 LA, even if it gets around the 'no hands' issue in the most unique way I've seen so far.