Chaser Wolf is the author of a Redwall yiff fic entitled "Shadow Rapes Matthias", which should tell you everything you need to know about both the content and skill level. This fic was the first of a trilogy, the other two being "Martin's First Time" and "Martin and Boar". These three fics were deleted shortly after their appearance, though they were saved and MSTed by Agents Laburnum and Foxglove with assistance from various Official Fanfiction University of Redwall characters. Also the author of "Donkey Devirginized", an equally unpleasant Shrek lemon.