Give this character a close or ranged combat action (minimum range value 4) that deals no damage. A successfully hit target becomes friendly to your force. Each target hit may be assigned one action as a free action, immediately after which the target becomes an opposing character again. Deal this character 1 unavoidable damage if the successfully hit targets’ combined point value is 150 points or more.
 

2012 Wording: Give this character a power action; it makes a close combat or ranged combat attack (minimum range value 4) as a free action that deals no damage. A successfully hit target becomes friendly to your force. Each target hit may be assigned one action as a free action, immediately after which the target becomes an opposing character again. Deal this character 1 unavoidable damage for each 100 points of the successfully hit targets’ combined point value.

•(Players Guide, 2014):  If a character affected by Mind Control KOs another opposing character, or is KOd itself, the controlling player receives the victory points.

When a character is affected by Mind Control, any of its powers previously countered remain countered. Powers and abilities that may only be used once per turn, round, or game may be used accordingly per Mind Controller.

A character that is successfully hit by Mind Control can’t use any game elements assigned to it during force construction until the Mind Control action resolves.

Since a character targeted with Mind Control returns to its previous controller’s force immediately after the free action resolves, any free actions that could be given to the targeted character “after actions resolve” can’t be given.

•(HeroClix Website 04-30-2013) There are three big changes here.  First, Mind Control is no longer activated by a power action.  Instead, it is activated with a close combat action or ranged combat action.  This means you can now use Mind Control with Charge or Running Shot (or any other effect that allows your character to take a close/ranged combat action).

Second, your Mind Control character will still take damage if you use it on expensive characters, but the threshold has been raised to 150 points instead of 100.

Third, and related to the previous point, your character will only ever take 1 unavoidable damage now when controlling large-point characters.   It does not matter if your Mind Controller controls 150 points or 1500 points: it will take only 1 unavoidable damage for doing so.

All of these changes serve to make Mind Control a much more formidable power.  I always found it very useful (who doesn’t enjoy using your opponent’s own force against him?), but using Mind Control is now much more flexible and combo-friendly AND the penalties for using it are much more forgivable.