Mutant Paint Brushes don't exist. There are Transmogrification Potions (obtainable via Random Events) that do exist that can turn your Neopet into the respective Mutant Neopet that the Transmogrification can turn it into.
Not at the moment... You can only get mutant from the lab ray.
A brown paint brush in Neopets is worth about 600,000 neopoints
You can use a mutant paintbrush. or use a Transmogrification potion that will automatically make it mutant. edit: There is no such thing as a mutant paint brush. So the only way is the tmp. (transmog potion)
You can get a free paint brush on neopets by either going to the giving tree or by trading with someone.
You can trade for them on the trading post or random events.
You buy one from a shop. Usually 40-50,000 neopoints.
that homeless guy over there does --> o<<
The starter can't be traded (sold, traded, auctioned, donated). so you have to either use it in the rainbow fountain ( located in Neopets Central)or discard it. The normal one can be traded or used or discarded.
Buy the baby paintbrush and then go to the rainbow pool and paint the desired pet.
To get a Mutant neopet, you need to give it the appropriate Transmogrification potion.
You should try the trading post. There are loads on there and although they are quite expensive, they are very worth it!
the lab ray- it's the same as jelly pets.