Can I react to Bewitching Spirit discard?

No, you cannot react to the discard effect of Bewitching Spirit specifically.

According to RiftJudge FAQ #10064, here is why:

1. Triggered Ability: When you play Bewitching Spirit, it enters the board (which does not use the chain). Its "When you play me" triggered ability then goes on the chain.
2. Response Window: You can react to the triggered ability itself using a Reaction card (as confirmed by RiftJudge FAQ #9894).
3. The Discard: When that triggered ability resolves, it instructs your opponent to discard a card. The discard is a game action that happens during the resolution of that ability.
4. No Interaction: Because discarding a card is not "playing" a card, and the card being discarded does not trigger an ability upon being discarded, your opponent cannot respond to the act of discarding. The card simply moves from the hand to the trash.

In summary: You can play a Reaction card to try to stop the Bewitching Spirit ability from resolving (e.g., by countering the ability if a card allows), but if the ability resolves, the discard happens immediately as part of that effect, and no further responses are possible during the discard process itself.