Multiattack

The drake makes two claw attacks and one stinger attack.

Claw

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage

In One Bite

Melee Weapon Attack: +7 to hit, reach 10 ft., one Tiny target. Hit: The target must succeed on a DC 15 Dexterity saving throw or be swallowed by the drake. While swallowed, the target's hit points are reduced to 0, and it is stable. If a creature remains swallowed for 1 minute, it dies. While it has a creature swallowed, the diminution drake can't reduce its size below Medium. If the diminution drake dies, a swallowed creature's hit points return to the amount it had before it was swallowed, and the creature falls prone in an unoccupied space within 5 feet of the drake.

Stinger

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d4 + 4) piercing damage, and the target must succeed on a DC 15 Constitution saving throw or have its size reduced by one category until it completes a short or long rest. This attack can reduce a creature's size to no smaller than Tiny.

Shrinking Breath (Recharge 5-6)

The drake exhales poison in a 15-foot-line that is 5 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw. On a failure, a creature takes 17 (5d6) poison damage and its size is reduced by one category until it completes a short or long rest. On a success, it takes half the damage and isn't reduced in size. This breath can reduce a creature's size to no smaller than Tiny.