Three Reasons to Reconsider Darkvision

With Darkvision being prevalent in many DnDish worlds, monsters of the darkness have evolved - or been bred - accordingly.

These aren't for any particular ruleset, though they lean towards 5e.

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Perilous Shade, by Clint Cearley, WotC

Created by the Derro, It-Stalks-In-Darkness is an insectoid horror that quickly broke free and bred true throughout the tunnels and caves of the Underdark.

It-Stalks-In-Darkness is feared because of its immunity to damage unless in the light - the brighter the light, the more vulnerable it becomes.  As might be expected, it never leaves the darkness of the Underdark.

An ambush predator if light is around, it prefers to drop down from above and drag its victims up and away from the group - anything to get away from the light.  In utter darkness, though, it will stand and fight with its scythe-like claws.

Given the chance, it prefers Dwarves and Drow over other species.  

In darkness, it is immune to normal weapons, but spells and magic weapons are normal.

In firelight, its AC is the equivalent of plate and shield.

In the spell light, its AC is like chain and shield.

In the spell daylight, its AC is like leather.

Damage comes from two attacks per round for nasty slicing and piercing damage.  Will try to pin a victim to the ground to gain advantage on attacks.

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Another such beast is the Luckeater.  Utterly invisible in darkness, it finds and follows any group of surface-dwellers, as their luck tastes better.  If seen at the edges of the light, it appears to be a 6-legged kitten, and mews piteously like one.  

Small and agile, the Luckeater is also lucky if fed.  All of its rolls are at advantage.

This is because it feeds on the luck of the followed group, leading to ALL rolls the individuals make being at disadvantage.

The best way to get rid of a Luckeater is to head outdoors - it won't venture outdoors under the sun or moon (but maybe on a horribly overcast night...).

If a group manages to slay and eat one, it is enough food for one person, and that person becomes lucky for the next 24 hours, rolling at advantage on everything.

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Nether Shadow, by Christopher Rush, WotC

Crafted from Shadows by Drow wizards as a counter to the Derro's It-Stalks-In-Darkness, the Darkdread has proven an effective instrument of terror, leading the way on Drow raids on Underdark communities.

The Darkdread creates an aura of paralyzing fear when seen through darkvision.  In torchlight, it lessens; in spell light, it lessens more; and in daylight the aura is dispelled entirely.

Being a product of corrupt Elven magic, true Elves of all sorts are immune to this fear, although half-elves and other Fae are not.

Mechanically speaking, Darkdread's paralysis is DC 24 in Darkness, DC 18 in torchlight, DC 12 in Light, and nonexistent in daylight. 

In all other cases, it functions as a Shadow, to include the Strength-draining touch.