Unit at Forbidding Waste is 4. I attack with unit that is 4. Their unit is 2 due to -2. They Switcharoo. Are they still 2?

Yes, the opponent's unit will no longer have the 2 Might it had before the Switcheroo resolved; its Might will have changed.

According to Rule 433.1, "Swapping" is the act of increasing one numeric value and decreasing another such that their values are reversed. Switcheroo targets two units at the same battlefield and swaps their current Might.

Here is how the interaction resolves:

1. Current State:
   • Your unit: 4 Might.
   • Opponent's unit: 2 Might (base 4, modified by -2 from the Forbidding Waste battlefield).
2. Playing Switcheroo: You target both units and play the spell. The chain closes.
3. Resolution:
   • Switcheroo calculates the current Might of both units (4 and 2).
   • It applies modifiers to both units so that their values are reversed.
   • Your unit becomes 2 Might.
   • Opponent's unit becomes 4 Might.

Important Note: The battlefield Forbidding Waste (which provides the -2 Might) is a continuous effect. Because Switcheroo applies a modifier to reach the target Might values, the -2 penalty from the battlefield continues to apply to the unit's final Might value.

• In this scenario, the opponent's unit effectively becomes 6 Might, but with the -2 modifier from the battlefield applied on top, its current Might is 4.
• Conversely, your unit would effectively become 0 Might, but with the battlefield effect applying only to the opponent's unit, your unit would effectively be at its new swapped value of 2.

This is my interpretation based on Rule 433.1 (Swapping) and FAQ #9335, which clarifies that Switcheroo uses current Might (including all modifiers) to determine the swap. No official FAQ exists for this exact interaction with Forbidding Waste.