I think its best to talk it over with whoever's involved beforehand. While dicerolling is fair (unless its me, because I always lose :V), it really can put a damper on your RP when you fail at something really simple. I think combat RP is best when everyone knows the end result beforehand, and things are planned out. That way, you don't have to completely trust that you or the other person won't just ruin things (intentionally or not).
OOC Transparency, as usual, is the key.
OOC Transparency, as usual, is the key.
