Hey, so they added the Shadow Initiate (assassin MC) feat to the compendium, even though it wasn't in the magazine.
Is it RPGA legal?
(/readies an action to Coup De Grace the first person to make a Warforged comment.)
Shadow Initiate is totally legal for play. It debuted in the Character Builder, thus it's good.
Sometimes, you just need to think about this from a common sense perspective - is there a good reason why it shouldn't be allowed?
Default for all content is it's allowed, unless we specify in either the content description or the Character Creation Guide that it isn't.