Here is my guide to a bunch of miscellaneous achievements early on in Bugsnax.
Fully transform a grumpus means to change all the body parts to bugsnax animals. This includes.
- Both feet
- Both legs
- Both hands
- Both arms
- Both horns
- Nose
- Head/hat
- Teeth
Once you do this, you can now change the body, which will change to the colour of the bugsnax. This unlocks the achievement.
*Note: I have been able to place a type of bugsnax, like say a strawberry on the foot. Then, I can place a different bugsnax on the foot, getting rid of the strawberry. I don't know if you can do this after they fully transform, but the grumpus I made is UGLYYYYY, so I hope so!*