This skill is exclusive for the Zephyr mage class.
"Wind Swap" is an ability that allows you to swap locations with a member of the enemy team. The only rule being, that the enemy you are targeting, cannot be inside the opposing teams castle.
The best way of going for this, is spawning as a Zephyr and getting as much EXP as possible until you unlock the skill. A good way of doing this is by activating a team skill before the game starts. Once the count-down hits zero for the game to start, activate a team skill and it should give you a boost to level 2, nearly 3.
Keep repeating this wind swap ability for 50 times and the achievement will eventually unlock on the score-board screen. There are no ways of checking how close you are to this, sadly.
Alternatively, spawning and dying will allow you to spawn stronger if you have 3000 Happy Stars. You can either spawn with 9 skills, thus giving you more chance of having the Wind swap ability, OR you can shorten cool-downs lvl4, which allows you to cast the ability more frequently; so really it's down to you. If you get it before you leave the castle, definitely use the Shorten Cooldown ability. (This is only in quick-match mode)
EDIT: In co-op you don't get those above "Spawn Stronger" Abilities. It seems you might want to possible outset your guy with an EXP buff to grant faster level ups. A pro is that it's a singular skill, so you don't need others to activate it.
EDIT 2: It appears there is an issue that some people are having with getting the skill to work. Some people are casting the spell and then it's cancelling itself for no clear reason. It has been suggested that you try doing the wind swaps on a bot and then following that bot around if possible.