Keen Senses. The Yellow Pseudodragon has advantage on Wisdom (Perception) checks that rely on sight, hearing, or smell.

Magic Resistance. The Yellow Pseudodragon has advantage on saving throws against spells and other magical effects. 

Limited Telepathy. The Yellow Pseudodragon can magically communicate simple ideas, emotions, and images telepathically with any creature within 100 feet of it that can understand a language.

Spell Casting. The Yellow Pseudodragon has 3, 1st level spell slots that can be regained on a long rest.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage, and 6 (1d6 + 2) radiant damage.

Poison Sting. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 4 (1d4 + 2) piercing damage, and the target must succeed on a DC 12 Constitution saving throw or become poisoned for 1 hour. If the saving throw fails by 5 or more, the target falls unconscious for the same duration, or until it takes damage or another creature uses an action to shake it awake.

Guiding Bolt. A flash of light streaks toward a creature of your choice within range. Make a ranged spell attack against the target. On a hit, the target takes 4d6 radiant damage, and the next attack roll made against this target before the end of your next turn has advantage, thanks to the mystical dim light glittering on the target until then.