When using Switcheroo on two units with the same might (like two Mundos), do they stay the same size? And how does Switcheroo interact with buffs on units?

Ruling: Switcheroo adds or subtracts might equal to the difference between the two units' current might values at the time the spell resolves. If two units have the same might, the difference is 0, so both units gain 0 might and remain unchanged.

Sequence:

• Calculate the difference between the two units' current might
• Apply that difference as a buff/debuff to each unit (one gains, one loses)
• The units don't literally swap might values, they gain or lose what's necessary to reach the other unit's might

Nuances:

• For Mundo specifically, if it receives a negative might modifier from Switcheroo, you must trash additional cards to increase its might back up (removing the negative modifiers one at a time: -6, -5, -4, etc.)
• Buffs on units are already factored into their current might when calculating the difference