Easily can but two packs way seems a bit more logical method to sort it out because icons regardless of the similar style can be used separately. Having one big pack which includes everything one game can include is both a very good and very bad things at the same time. I will decide later. I will look on how many icons and tiles I will have in the end.
Maybe if the slime will be animated (with a full set: jump, hurt, death, a bunch of attacks) it deserves separate pack...
Additionally icons in 16x16 format and other things in 32x32