The “Subdivision Surface” or “Subsurf” modifier basically takes all the polygons in your model and subdivides them, increasing the poly count but making your model smoother at the same time.
We’ve already added a mirror modifier so go ahead and add the Subsurf modifier and change the settings to this:
Having the “View” and “Render” number the same means that what we see while editing, is what it will be when complete. Having the modifier apply to the editing cage allows us to see the shape a bit more easily:
Our model is looking pretty good, but those subdivisions have contorted the little guy away from the reference images…a bit of scaling, vertex movement and maybe some new edge loops should fix that:
Once you’re happy that the modifiers have produced a good mesh then feel free to apply them (importantly…do it in the right order!) I suggest keeping a copy of your model prior to that application though in case you want to go back and make adjustments later.
So let’s now make an appropriate mouth…