The first thing that a modder should do upon creating a new creature, even before posting it in a topic like this, is to start up Arena Mode and check the error log in your DF folder. In this case, the error log shows the following error message:
Unrecognized Skill Token: PUNCH
Unrecognized Skill Token: KICK
This is a fairly simple error to fix; merely replacing those tokens in the attack bits with GRASP_STRIKE and STANCE_STRIKE, respectively, should fix it up. After exiting from DF, we clear the error log to reduce clutter and fix those.
Now we start up DF again and return to arena mode to double-check the log. This time, the error log is free of messages, so that's a good start. The error log is a great place to find basic syntax errors like this. It's usually self-explanatory, though there's some situations like this where you may need to get help from the forums.
Aside from that, some other suggestions:
-The creature lacks the LARGE_ROAMING tag. You might want to put that there. This looks like a copy of the bronze colossus with some modifications, so there might be some other important tags you're missing that escape me at the moment.
-Putting a FREQUENCY:n tag on there may or may not be a good idea. Default is 50, can be from 0 to 100, you can put that tag there to make it more or less common than usual.
-BODY_SIZE is a little small. For comparison, dogs are three times as big.
-This creature may be indestructible at the moment due to inherent flaws in the material/tissue/combat overhaul. Not much you can do about that at the moment, aside from removing NOTHOUGHT and adding a brain.