If my bird token is at forbidden waste defending alone, and I use discipline, what is its might after the spell resolves?

The Bird token ends at 1 Might.

Sequence: Bird token has base Might 1. Discipline gives it +2 (increases apply first), and Forbidding Waste's passive gives it −2 while defending alone (decreases apply last). 1 + 2 − 2 = 1 Might. Because Forbidding Waste's effect is a passive, it applies continuously and isn't snapshotted away by the buff (Rules 477.3.e, 477.3.b). If it somehow stopped defending alone later this turn, it would keep the +2 from Discipline for the turn and sit at 3.