I recently finished a commission for the minion warlock duo Rorsh and Brine. This pair of pigs has gotten very muddy in their fights:
For the weathering effects on these two, I added quite a bit of mud splatter, and made the base a little glossy by simply adding some 'ard coat. The mud on the mini comes from a brown glaze over the lower parts of Brine. The splatter itself if a slightly thicker glaze put on the brush near the mini, and blown onto the mini (hold the brush to your mouth and blow). I often use the same technique to apply blood splattering on miniatures, since it gives you a very realistic look.
Normally, I wouldn't apply quite so much mud, but it just seemed so right.
With this pair finished, the only minion warlock I haven't painted is the dwarf and polarbear combo Brun Cragback and Lug.