It is widely believed that the owlbear is the product of a biomancer's attempt at a chimeric fusion. An owlbear, a creature that combines the aggression of a bear with the  irascibility of an owl, is already anything but docile. The influence of the Plane of Fey, home of the suneater owlbear, has done nothing to bridle these extreme emotions. In fact, these owlbears are more territorial, more grouchy, and more ravenous than their Material Plane counterparts. 

Catch the Sun. The suneater owlbear can feed on sunlight. It dislocates  its huge maw to reveal the photosynthetic pigments specially-adapted to catching the hues of light shed by the Plane of Fey's eternal sunset. One should avoid exposed outcroppings of rock in the Plane of Fey; these vantage points are often a suneater owlbear's dinner table, and suneaters are extremely territorial.

By comparison, the bright daylight of the Material Plane is a feast, albeit an ephemeral one. The suneater owlbear is used to a constant food supply and the diurnal cycle to which so many Material Plane beasts are adapted leaves a particularly hangry and irritable. 

Indolent and Iridescent. The term Batesian mimicry comes from the dungeoneer Bates Buttonchop who would disguise himself as a black pudding in order to loot monster-filled crypts. The dungeon natives would avoid Bates' disguise, having been stung by puddings before, leaving him free to pulion all manner of precious teasures. Suneater owlbears, who're vulnerable in their darkened caves, use this Batesian mimicry to appear like observers, dangerous eye-tyrants from The Low. This combination of above-ground ferocity and below-ground intimidation has proved quite the survival strategy

Lair Actions. On initiative count 20 (losing initiative ties), the owlbear takes one of the following lair actions; the owlbear can't take the same lair action two rounds in a row. See the table above for the damage and save DC.

Rage. The owlbear's territorial rage affects all other creatures within the lair. Each creature must succeed on a 11 Wisdom Saving throw or immediately use its reaction to make one weapon attack against a random creature within reach/range. 

Disorienting Lights. Flares and sparkles erupt in a deluge, confusing and disorienting creatures. Each creature in the lair other than the owlbear must succeed on a 11 Constitution saving throw or be affected by the confusion spell until the end of its next turn. 

Summon Sunsprites. A sunsprite appears next to each creature of the owlbear's choice that it can see and disappears on initiative count 20 of the following round. The sunsprites act on initiative count 10 of this round. They have an attack modifier equal to +3, the saving throw of their Death Burst is DC 11 Dex Save, and both its attacks and Death Burst deal 3 (1d6) radiant damage, instead of their normal statistics.