Does the new Disintegrate errata 'Deal 3 to a unit at a battlefield. If this kills it, do this: draw 1' work within the rules, specifically regarding when the conditional reflexive trigger checks if the unit was killed?

Ruling: Disintegrate works as intended. The conditional reflexive trigger should be treated as a delayed triggered ability that checks whether the unit died from the spell damage during the cleanup step immediately following the spell's resolution.

Sequence:

• Play Disintegrate
• It deals 3 damage and creates a conditional reflexive trigger
• Cleanup occurs
• During cleanup, the unit dies from lethal damage
• The delayed trigger condition is met and goes on the chain
• The draw effect resolves and you draw 1

Nuances:

• The ability doesn't use typical delayed trigger templating (like "when" or referencing a specific time), but should still be treated as a delayed trigger whose timeframe is implicitly "the cleanup following this spell"
• The templating is considered suboptimal - it would work better as an explicit delayed trigger or as an unconditional reflexive ("Then do this: If it killed it, draw 1")
• If the unit is removed by other means (like Hidden Blade) before cleanup, you do not draw because Disintegrate didn't kill it