Pit Rookie goes in Forbidding waste to Tideturner that has hidden switcheroo as defender. How much might have each unit after resolving of switcheroo if pit rookie is an attacker?

Pit Rookie ends at 0 Might, and Tideturner ends at 2 Might.

Tideturner is defending alone at Forbidding Waste, so its current Might when Switcheroo resolves is 0 (base 2, −2 from the battlefield). Switcheroo swaps current values (Rule 433.1.b): the difference is 2, so the lower unit (Tideturner, 0) gains +2 and the higher (Pit Rookie, 2) loses 2. Forbidding Waste is a "while" static effect that keeps re-applying, so Tideturner ends at 2 + 2 (swap) − 2 (penalty) = 2, and Pit Rookie at 2 − 2 = 0 (FAQ #12532).

Practical note: at the Combat Damage Step each unit assigns damage equal to its current Might, so Pit Rookie deals 0 and Tideturner deals 2 — Pit Rookie dies. The swap modifiers only last this turn, and if Tideturner stops being alone the −2 falls off (it would then be 4).