What happens if you have an action that lowers your DX on your turn?

[Skarg]

Originally Posted by Rick_Smith

That never happens in the campaigns around here because the big critter actually has to attack you, to lock in the defend option. Until someone pays the penalty caused by your defending, you have not taken that option.

Yep, that's how we do/did it too. When a figure's turn to actually act comes and they declare an action, they can no longer change their mind - they're doing it. People can react that to that by defending or dodging.