Binary. The Bug can only roll a 1 or a 20 on the d20.

Elusive.  If the Bug is subjected to an effect that allows it to make a saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Multiplicative Nature. As long as there is at least one Bug in existence, when one Bug is killed, five more Bugs spring into existence somewhere in the world.

Nimble Escape. The Bug can take the hide or disengage action as a bonus action.

Innate Spellcasting. The Bug's spellcasting ability is constitution (spell save DC 16). It can cast the following spells, requiring no material, somatic or verbal components:

• at will: mind sliver, vicious mockery
• 1/day: hold monster, immovable object,  modify memory, slow, wall of force

Touch of Malfunction. Any machine or other mechanical device the bug touches starts to malfunction in one way or another. It might simply stop working, but it might also freeze, overheat or otherwise behave erratically.

Endless Loop of Attacks. The Bug repeats its Glitch attack, until it scores a hit. It then uses its Surge of Malfunction.

Glitch. Melee spell attack, +8 to hit, reach 5 ft., one target. Hit: 10 (3d6) force damage. A creature hit by that attack must make  a DC 16 intelligence saving throw. On a failure, roll 1d4 to determine what happens to it:

• The creature carries an invisible, heavy object for the next minute, occupying both hands and forcing it to move at half its speed. The creature can't get rid of the object, even if it tries to throw it or put it down.
• The creature loses access to its inventory and equipped items for the next minute. The only item it still has is a basic set of clothing it wears. When the effect ends, it regains access to its inventory and all equipped items and armor reappear on its body.
• The creature ignores collision for the next minute. It can move in all directions, including up and down, through solid objects and other creatures; but it can no longer interact with the  world or with other creatures.
• The creature freezes in place and is paralyzed for the next minute.

The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.

Surge of Malfunction. Each creature within 20 feet of the Bug must make a DC 16 intelligence saving throw. On a failure, the creature suffers malfunctions for 1 minute, as if it was affected by the confusion spell. In addition, if it casts a spell, it automatically triggers a Wild Magic Surge.

It can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

If ithe creature succeeds on the save, it is immune to this Bug's Surge of Malfunction for the next 24 hours.

Stack Overflow. If the Bug is about to take 30 or more damage from a single instance, it can use its reaction to prevent that damage being subtracted from its HP.  The creature that caused that damage must make a DC 16 intelligence saving throw or is paralyzed until the end of its next turn.