Guys, the mermaids seem endless, so just kill the pirates and the mermaids will back off.
In response to Gajin:
Maybe a ten sided dice. 1 being epic fail, 2-3 being fail , 4-5 being a not very bad fail, 6-7 being a success, but not a way good success, 8-9 being an extra special success, and 10 being an epic success, like you do everything even better than you originally posted