Hi Brutalrage,
One of skaven's biggest weaknesses is that most warriors have low leadership. Therefore undead warbands and any warriors that cause fear are a great way to attack this weakness. Remembering to apply All Alone tests when fighting is also a good idea (this rule is forgotten by many groups) although if your skaven opponent plays well then they will be able to use the often superior numbers in their warband to limit the effect of All Alone tests.
Perhaps also playing some of the different scenarios that out there can not only increase the variety of your battles (which is fun) but can provide other opportunities where skaven need to face their biggest weakness. Examples are the Haunted Wreck from Fanatic Issue 79 or the Spawn Hunting scenario from Fanatic Issue 86 (both can be found on the
Fanatic Online section of this web site) both have fear causing NPCs (well it isn't explicitly mentioned in the Haunted Wreck but the 'undead' special rule would be short-hand for the following rules that generally apply to all/most undead: cause fear, may not run, immune to psychology, immune to poison). There are many, many other scenarios out there. Of course if you are going to add new scenarios then don't just add scenarios that are bad for skaven but add scenarios that are bad for your warband also or bad / good for everyone just to be fair!
Remember the main thing with adding scenarios (and playing Mordheim in general) is just to have fun!!
I hope that this helps,
RL
