If I hook a Mixologist, do I have to do the hook first and pick a unit and then resolve the Deathknell and choose the unit from Mixologist? Or do I choose Mixologist unit before the hook action?
To resolve this interaction, you follow the rules of the chain (LIFO - Last In, First Out) and the specific timing of the Baited Hook and Glasc Mixologist's Deathknell ability.
The Short Answer
You do not make a choice for the Deathknell until it resolves.
When you activate Baited Hook, you target the Glasc Mixologist to be killed. You do not choose a unit for the Deathknell effect while activating the hook. You only make choices for the Deathknell effect when that specific ability later resolves from the chain.
Sequence of Resolution
- Activation: You activate Baited Hook, paying the costs and targeting your friendly Glasc Mixologist.
- Resolution Begins: Baited Hook begins to resolve. It kills the Glasc Mixologist.
- Deathknell Trigger: Because Glasc Mixologist has Deathknell, its trigger is added to the chain as a "pending item" immediately when it is killed (Rule 428.1.a.1.b).
- Baited Hook Continues: Baited Hook continues its instructions: you look at the top 5 cards of your main deck and may play a unit from among them.
- Chain Resolution (LIFO): Once Baited Hook finishes its instructions, the chain checks for pending items. The Deathknell trigger is the next item on the chain.
- Deathknell Resolves: You finally resolve the Glasc Mixologist's Deathknell ability. Only at this moment do you choose a unit with cost 3 or less from your trash to play to the battlefield.
Important Note on Targets
- Baited Hook: The target for the hook must be chosen at the time of activation (when you pay the costs and put the ability on the chain).
- Deathknell: The target for the Deathknell ability is chosen upon resolution of that ability.
Because of this, you will know the outcome of the Baited Hook's top-5-card reveal before you have to commit to which unit you are playing from your trash with the Glasc Mixologist's Deathknell.