Hi A100N, you are going into deep waters now
You can't resize a model unless you resize the animation also, because the model will scale to the animation when it plays, and it will look like nothing has happened, like in your case.
And you can't really resize an animation for a monster because it will throw the grid system off, if you scale it down by 50% the monster will walk half a tile, and if you scale it up by 150% it will walk one and a half tile, and then gets weirdly snapped back/fourth to the rest pose on a new tile it was trying to move to.
The only way to get this right is to recreate the animation for the monster so that it matches the grid tiles of the game.
If you take a look at the TinyCritterController class (the harmless spider and crabs) they have their own models and their own animations, there is no magic setSize command or scale command, so to the best of my knowledge you will have to do this from the ground up.
Kind regards.
Skuggasveinn.