Following my first thoughts, I did a quick search of the D&D Compendium and found to my delight that there are precisely four powers in all of Fourth Edition (for player characters) that make use of the [Sleep] tag. One for the Wizard (Sleep), one for the Bard (Whispers of the Dream King), one for the Seeker (Wave of Sleep), and one for the Swordmage (Waves of Languor). The four powers vary only slightly in their basic utility and application.

The “core” Sleep effect seems to inflict target(s) with the Slow condition (saving throw ends the effect), and then renders the target(s) Unconscious after they fail their first saving throw. Two of the powers target the Fortitude defense, and the other two target the Will defense. I’ll make a handful of Reflex-targeting Sleep effects to reflect the Hypnotist’s use of “dust” powers to cause drowsiness and fatigue, but I’ll make sure to mix it up.

I’m going to aim to have at least one Sleep power per level for the class: Encounter powers at 1st, 3rd, and 7th and Daily powers at 1st, 5th, and 9th (for now, I’m only concerned with the first 10 levels of the class). Not sure what I’m going to do about Utility powers at 2nd, 6th, and 10th, though. I’m picturing the Hypnotist as a combination of the Sandman, some type of charlatan, a carnival or sideshow magician with a dark side — there’s the Beguiler class (Player’s Handbook 2) from 3.5 to draw ideas from, for sure.