Here’s an easy idea from The Anticraft: Festive eyeball ornaments!*

Their instructions call for making the eyes out of polymer clay, but you could get a fairly similar effect more easily by just painting eyeballs on round white ornaments.

You could do a whole treeful of different eyes: Reptilian pupils, Eyes of Sauron, yellow zombie eyes, bloodshot monster eyes…you get the idea. Embellish with fake-fur “eyelashes” or whatever adornment seems appropriate and your tree can watch your every move.

*Eyeball ornaments are festive, right?