Gar is easily one of my favorite characters in comics and through the years I have met many people who hold him in the same high regards. However even tho we all love the character, one thing I find people always split on is whether Gar should be able to turn into non natural animals. 
 
Now Gar's basic power set is that he can take the form of any animal, as a result of the life saving experiment his parents performed on him integrating and fusing his dna with that of animals in Earth's geen poole.  However under different writers these powers can be very literal or abstract.  During "Titans" Winick had him rtansforming into things giant tarantulas and even a anthropomorphic goat once (tho I hope that was just for visual effect and not meant to be taken very seriously) During Hendersen's trian wreck of a run (my opinion and I'll stand by it) She had him turning into centaurs, dragons, phoenixes and a Copy of the amalgamated creature the Wyld. 
 
Personally I think Gar should be limited to only natural, Earthling animals. I say earthling animals to exclude animals from other planets and life-forms from earth oputside the animal kindom (that's right, no amoeba's as they are in the The Protazoan Kingdom)  I feel this way for two main reasons. 
 
One, it's simply makes more sense with his origin.  He was given his powers through science specifically using natural DNA codes.  Mythical creatures originate from magic and therefore don't work biologically work like real animals do.  All the things that mythical creature can do, like a dragon breathing fire or a phoenix ressurecting are abilities granted by magic and therefore should be things that are out of Gar's bounds.  Also when it comes to enlarging a pre-exiting animal or taking parts from many animals to create an amalgamated form the same biological limits aply.  Animals a structered to work in the size they are, change that and their can be organ failuer or the body itself won't be able to hold together. And mixing and matching pieces of other animals causes all sorts of issues with how the peices would fit internally.  A lion heart won't have the right peramiters to pump blood to a gorilla arm (or any combination you wish) 
 
My second problem with him turning into non-natural creatures is that it makes the writers lazy and he doesn't need it to be an effective character.  The animal kingdom is so diverse (with so many amazing abilities) that he should never need to turn into anything else.  Besides if he can turn into things like a dragon, why would he ever be things like a dinosaur? 
 
So what do you guys think?

i totally agree with you. yeah it's cool to be able to turn into fake animals but it doesn't make sense and it makes it to easy for him to win.

It seems that his state of mind affects whether the animal forms he takes are real or not. When healthy, he tends to stick to real animals. When he got exposed to mento's helmet though, he was turning into mythical beasts and all sorts of crazy things. I think this was a fantastic way to confront this possibility within his powers.

yes