get a smaller blenny. the lawnmower is aggressive and hard to keep fed. beginner corals are pretty safe. people usually only have issues when chopping them up without protection. try a Zoanthus. they are easy. just put it on a rock in the light and near the flow. mushrooms may be even easier.
wennerae sold at http://tampabaysaltwater.com/ordering/pricelist.html
care info:
http://www.ucmp.berkeley.edu/arthropoda ... #directory
any of the small mantis' would be fine.