Recently i find new smartphone game - Seven Knights (세븐나이츠). It tactical rpg with very good graphic and it full free. Only on Korean language atm.

Seven Knights
Game future PVE and PVP modes http://www.youtube.com/watch?v=5xjJ6m2ukjc with really addictive gameplay.
Google play - https://play.google.com/store/apps/details?id=com.cjenm.sknights
iOS - https://itunes.apple.com/us/app/sebeunnaicheu-for-kakao/id741949324?mt=8
Facebook fan group - https://www.facebook.com/groups/7KnightsGame/
Seven Knights - Best Mobile Online RPG
Donate
You can easy get donate gems just by little grinding and there not much things that really worth. 250 gems - 10 random 3-6 star cards, most time it going be only 3 star card. Costumes cost 150-300 gems but most of them look bad for me. There also passive player skills that cost gems but they give not much and i not sure how they work atm. You also can buy keys for gems to play in dungeons but they cost almost free. For 150 gems you can run again in elemental dungeon, be sure that you doing it in right day.