Thanks for the correction. I usually check for the correct spelling of character's names, but I haven't watched Rocko for ages, so missed that Heffer was spelled differently (also, the original requester used "heifer"). I'll fix it in the description.
Given that this picture dates back to 2011, most of what you've described was unknown when I drew this.
However, at the time I felt that Mordecai was more laid back like Jake, while Rigby was more energetic like Finn. It was also more amusing to me to play against the obvious Mordecai/Finn = tall and Rigby/Jake = short correlation.
I'm aiming to get Experience the Magic of the Legend! Vol 2 out for Thought Bubble, so it was my intention to give one ACEO away with every purchase of Vol 1 & 2 together (or Vol 2 with proof of purchase of Vol 1). I suspect the cuter/saucier ones will go first, so it's possible it will still be there by the time you get to us.