If some plays Darius then Fizz and then activates Fizz effect do they miss the timing to ready Darius?
No, you do not miss the timing to ready Darius, Trifarian in that sequence. Darius will successfully trigger and become ready.
The Sequence
- Play Darius, Trifarian (1st card): He enters the battlefield.
- Play Fizz, Trickster (2nd card): Fizz enters the battlefield.
- Trigger Condition Met: Because Fizz is the second card played this turn, Darius's ability triggers.
- According to RiftJudge FAQ #9173 and #11030, since Darius is already on the board when the second card of the turn is played, he sees that the condition has been met and triggers his ability, gaining +2 Might and readying himself.
- Fizz's "When you play me" (WYPM) Ability: After Fizz enters play, his WYPM ability is placed on the chain.
- Activate Fizz's Ability: You resolve Fizz's ability to play a spell from your trash.
Why this works
The "second card" condition is checked immediately when the second card (Fizz) resolves and enters the board. Darius triggers at that moment, regardless of what abilities Fizz might have or what you do afterward. The fact that playing a spell via Fizz counts as a "third card" played later in the turn does not retroactively negate the fact that Darius already triggered when Fizz (the second card) was played.
Note: This interpretation is based on the mechanics of triggered abilities (Rule 383) and established RiftJudge FAQs regarding Darius, Trifarian (specifically FAQ #9173 and #11030). If you have further questions about specific interactions, feel free to ask!