I converted this old Skaven lineman to have a chainsaw. This is illegal in Bloodbowl but is quasi legal at times. I made the Chainsaw out of two plastic space marine chainswords, the axe handle from a plastic space marine power axe and some bit from I think an Ork plastic vehicle sprue.
Although the model looks good, the chainsaw isn't particularly effective in the game. You first have to start it, then once you get it going if you fail a block or someone blocks you will be cut to peices yourself. Plus you will likely be sent off for cheating too. All in all I wouldn't add a Skaven with a chainsaw to a Bloodbowl team until you have almost everything else. With Goblins it is different, they are cheaper and you expect them to die. With Skaven you die easily but you can also score a lot of points, an Ork team with Goblins can afford to just spend a drive or a half beating up the opposition. With a Skaven team you always have to try to get the ball and score. Unfortunately the more you score sometimes, your opponent just gives up trying to win and concentrates on beating up your team anyway. It is tough to play a Skaven Bloodbowl team and Rat Ogres and or illegal weapons are not the answer. The answer is lying down and playing dead.
The longer a Bloodbowl league goes the more it favours Orks, Chaos, and Undead. The Undead used to regenerate on a 4+. I've often thought of trying to get regenerate as a mutation but it is tough to pull off and I still can fail the roll. I've failed key doctor rolls before.