The move element of Dragon's Tail is:
- Move : Swap places with target
Duergar have Stand your Ground:
- Stand Your Ground: When an effect forces you to move — through a pull, a push, or a slide — you can move 1 square less than the effect specifies. This means an effect that normally pulls, pushes, or slides a target 1 square does not force you to move unless you want to.
I contend that the 'swap' is not a pull, push or slide and therefore SYG does not apply as a defense against it.