Once per round, before making your first attack, you may choose to teleport momentarily to a position opposite you opponent and attack from there. Immediately after, you return to your original position. This first attack gains a +2 flanking bonus, and if you have at least two attacks, your second attack gets a +2 flanking bonus, too. Any further attacks that round are treated normally.
Alternately, you may use this power defensively. During one attack per round, you may choose to momentarily teleport away and back, giving your opponent a 50% miss chance.
The offensive use of the power has no benefit if a friend of yours is already flanking your opponent, since that already gives you a +2 flanking bonus on every attack.