Falling star glass mixologists

Two 3-damage instances, one chain item — so nobody gets a reaction window between them, and a Glasc Mixologist only dies if it eats both.

Falling Star was errata'd to "Deal 3 to a unit. Deal 3 to a unit." — two separate instances inside a single spell. It resolves as one chain item, executing both instructions back to back with no pause for reactions (FAQ #8639, #12407); the only windows are before the spell resolves, and afterward when the death trigger goes on the chain. Mixologist is 5 might, so one instance (3 damage) leaves it alive and its Deathknell never fires — you need both instances pointed at it for 6 total.

Once it actually dies, Deathknell is added to the chain as a Pending Item before the card is moved to the trash (Rule 808.1.d.2), and because the chain is closed at that point players do get to react to the trigger itself (FAQ #10991). When it resolves you may play a unit costing no more than [3] and no more than [A] from your trash ignoring its cost — it enters fresh with no damage marked, and it does not enter ready (FAQ #10696, #12569).