War Caster

You've practiced casting powers in the midst of combat, learning techniques that grant you the following benefits:

• You have advantage on Constitution saving throws that you make to maintain your concentration on a power when you take damage.
• Once per round, when a hostile creature provokes an opportunity attack from you, you can use your reaction to cast a power at the creature, rather than making an opportunity attack. The power must have a casting time of 1 action and must target only that creature.