When playing Arcane Shift on Fizz, what resolves first, the 3 damage or the Fizz ETB?

When playing Arcane Shift targeting your own Fizz, Trickster, the 3 damage dealt by Arcane Shift resolves before Fizz’s "When you play me" (WYPM) ability.

According to RiftJudge FAQ #8499 and Rule 157.3.a, a spell or ability must finish resolving all its instructions in their entirety before any other chain items (including triggered abilities that were added during that resolution) can begin their own resolution.

The Resolution Sequence:

1. Cast Arcane Shift: You target your Fizz and an enemy unit. Arcane Shift becomes a Finalized Chain Item.
2. Banish Fizz: As Arcane Shift begins resolving, its first instruction moves Fizz from the board to the Banishment zone.
3. Play Fizz: Arcane Shift's second instruction moves Fizz from Banishment back to a battlefield.
4. Fizz Triggers (WYPM): The moment Fizz is played, his "When you play me..." ability triggers and is added to the chain as a Pending Item on top of the still-resolving Arcane Shift.
5. Deal Damage: Because Arcane Shift is still resolving, it continues with its next instruction and deals 3 damage to the targeted enemy unit.
6. Arcane Shift Banishes: The final instruction of Arcane Shift is to banish itself. Arcane Shift leaves the chain.
7. Fizz Ability Resolves: Now that Arcane Shift has finished resolving and left the chain, Fizz’s WYPM ability is the newest item on the chain and begins its resolution. You now choose a spell in your trash to play.

Key Timing:

• Triggering vs. Resolving: Fizz's ability is added to the chain during the resolution of Arcane Shift (Step 4), but it cannot begin its own resolution until the spell that triggered it finishes executing all of its instructions (Step 7).
• Targeting: Per RiftJudge FAQ #10020, you choose the target spell in your trash the moment you add Fizz's triggered ability to the chain, but you do not play that spell until the ability itself resolves in Step 7.