I like the colors on these! But I'm not sure if the normal pig is fitting in

With your troll there are a few problems.  It looks awesome dont get me wrong.  The first thing that i notice is that the dithering is not necessary at all, if anything it is overkill.  Dithering shouldnt be used in this case especially with so many colours.  Dithering should be used for texture or shading when the colour pallette is very limited.  There are of course exceptions to this idea but it takes a great deal of skill to know when.  The problem with the dithering in this case is that on the skin the colours that you used in the palette are very numerous it makes the troll look much to smooth in the way that you wouldnt want. 

There are also some banding issues, heres a good thread on it http://wayofthepixel.net/index.php?topic=8110.20.  The place that i see the most of this (because i am still a novice to it as well) is in the shading of the hand and the ear.  The background looks awesome but watch that it looks like you drew everything on the same layer because the tree seems to warp around the hand as if you were afraid to draw through it or didnt want to hide it behind. 

The colour scheme as well as the composition are a bit odd depending on what you are trying to portray.  If you want the skull to be the focal point (because thats what me thinks) then there should be much more contrast on the skull with potentially speculars and a darker background behind it.  Another part of the composition and colour is that the palette is a bit random.  The colours dont go very well with themselves.  The background is too bright and tries to steal the attention from the troll and his precious.  Also the tree background should part behind the skull if thats what you want so you get rim light on the hand then hand shadow then a highly contrasting skull.

Another detail is the lighting.  The piece lacks a strong light source to drive it that extra mile and make it even more awesome.  I think a great idea would be to put the light source from the break in the trees behind him so that the light source is a rim light but we also get a top down secondary due to the slight breaks in the decayed canopy.  You showed that you cacn easily do the latter on the ear the way it is lit slightly more sky blue than the rest of the body. 

The final thing is the perspective.  The way you portrayed it doesnt quite make sense where it is dismissing to a one point perspective on the horizon but the trees seem to be vanishing downhill.  This is supported by the ability to see the roots of the tree in the midground aswell as the background which then sinks off.  It is definitely possible but very unusual.  I also wanted to add that you dont ave to muddy out your colours like the sky for example since its pixel art it can be bright and poppy and still be able to maintain the fantasy world gloom.

Sorry to almost sound discouraging with the super long info dump of mine but hopefully you read through it all and understood what i was trying to say.  I completely understand that some choices were stylistic and dont worry about what i said if so.  If anything i said was straight out wrong please do not hesitate to let me know so that i dont keep telling people how to do things wrong.