As an Action you can transform into any beast inn the Players Handbook, or approved home-brew by the DM. Your size stays Medium when in beast mode as do your stats including health.  When in Beast Mode, you gain the attack features of the beast but if there is a bonus effect for sized creatures they are void.[Example, if you became a Tyrannosaurus rex, you remain a medium creature and yours stats do not change, and you gain it's Bite and Tail attack {4d12+STR mod & 3d8+STR mod respectively} but you cannot grapple with a bite.]

When hit by a Critical it by an attacking creature, it as a chance to strike and damage the cog. When it wit a critical hit, the DM rolls a d100, on an 85 or higher, the cog is damaged. If the cog is damaged wile in Beast mode, you MUST spend your next action to de-transform. To repair it, two hours must be spent to repair it. To make the repair in time, a general intelligence check wit a DC of 8+your constitution Modifier+Proficiency. On a failed save, the repairs take an extra half hour and the check must be made again. The maximum time it takes to repair is 8 hours, being the time of a long rest.

To sustain yourself you now require rations. This is because the Transformation Cog in a powerful upgrade, and requires that your fuel be replaced each day.

Once per day as a bonus Action you can overcharge giving yourself advantage on Strength Saving throw for one minute