If my opponent uses Challenge, then I use Discipline, can I resolve Discipline then play another Discipline before Challenge resolves?

Yes, you can resolve the first Discipline to draw a card and then play a second Discipline before the Challenge resolves.

Reasoning

This interaction is covered by RiftJudge FAQ #4745. According to the game's timing rules for the chain:

1. Chain State: When your opponent plays Challenge (Action) and you respond with Discipline (Reaction), the chain is formed (bottom to top):
   • Bottom: Challenge
   • Top: Discipline
2. Resolution Process: The chain resolves from the top down.
   • The first Discipline resolves, granting your unit +2 Might and allowing you to draw a card.
3. Timing Window: After an item on the chain resolves, the chain is not immediately empty if other items (like Challenge) remain. Before the next item resolves, both players are given an opportunity to react.
4. Playing the Second Card: Because you have drawn a card from the first Discipline, you can play that second Discipline (as a [Reaction]) during this priority window before Challenge resolves.

Sequence:

• Opponent plays Challenge (Chain is now Closed).
• You play Discipline (Chain: Challenge, Discipline).
• Discipline resolves: You gain +2 Might and draw a card.
• Priority Window: Because Challenge is still on the chain, both players have the opportunity to react. You may now play your second Discipline.
• Challenge resolves: Finally, the Challenge resolves once both players have passed priority.

According to Rule 340.4, when the chain is not empty and there are no pending items, the controller of the newest item on the chain gains priority, allowing for these sequential reactions.