I used Thrill of the Hunt on Darius Trifarian. It's my first card, does his ability take effect and ready?

Yes, playing Darius, Trifarian via the resolution of Thrill of the Hunt when it is the first card played in your turn will trigger his ability.

Analysis of the Sequence

1. Playing the Spell: You play Thrill of the Hunt as your first card this turn.
2. Resolution: As part of the resolution of Thrill of the Hunt, you banish a unit and then play Darius to a battlefield.
3. Determining Card Order:
   • According to Rule 419.4.a, a card is considered "played" once its effects have fully resolved.
   • Since Thrill of the Hunt was the first card initiated, it remains the first card played in the sequence.
   • Darius entering the board via this effect means he is the second card played in the turn.
4. Trigger Condition: As established in RiftJudge FAQ #10800, playing a card via a game effect counts as playing a card. Because Darius is the second card played this turn, he enters the board and his ability triggers.

Important Notes

• Gear Detachment: Per RiftJudge FAQ #10792, when a unit leaves the board to be banished by Thrill of the Hunt, any gear previously attached to it detaches and remains at the previous location, as the unit is moving from a board zone to a non-board zone.
• State of Entry: Per RiftJudge FAQ #10792, a unit played via Thrill of the Hunt enters the battlefield exhausted by default. However, because Darius's ability triggers upon being the second card played, his ability will resolve and ready him.
• FAQ Clarification: The mechanics regarding gear detachment are derived from game mechanics discussed in RiftJudge FAQ #2960 and #10792, which state that gear falls off when a unit leaves the board.