The rumors ended up being true as the new teaser page for the 9th character Arisha just went live on the official Mabinogi Heroes website. According to data miners the new character is a hybrid melee and magic user. The trailer doesn't reveal much other than her figure shown off in a faint black silhouette near the end.
Game Site KR: http://heroes.nexon.com/promotion/summer14/arisha.html
Game Site EN: http://vindictus.nexon.net/