Ahh gentlemen first of all good luck i hope you do well. Derek and i lost out to these guys in the semis and i know what their army can do but being a fair and sporting player i wont divulge their secret stuff in the name of fair play, but i can offer some advice that is useful against any other de army.
Watch out for the harpy/dark rider redirection trick. They will try and pull your furnace all over theboard especially into difficult ground. Screen your arcs so that you can only go forward.
Dont deploy behind your animosity orcs as they will stutter your plans.
Keep furnace in the centre so that if redirected you are still around in the action.
The black guard can be very nasty with loads of hellish tricks and gizmos. Remember elves are only t3 (nudge nudge wink wink)
Concentrate all firepower on that super star destroyer (sorry got carried away), work out what the greatest threats to your army are and work on neutralising these as a priority. Ie vs horde armies are 6 bolt shots gonna do much damage? How about if they have many bolt throwers? Do their knights, chariots infantry blocks gonna cause you trouble. Zero in your efforts on these units and weaken them if not destroying them.
Fight fire with fire, warmachines vs warmachines, infantry blocks vs inf blocks but always try and get the advantage with flankers or having earlier weakened them.
Basically get your furnace and/or grimgors units into combat along with hellpit (if it survives the storm, quite a big priority target for them!) and the elves will struggle to deal with all that power and madness.
Let them dictate the game with shooting and redirection and you will find it very hard. Simon and tom are very good generals but you are in the final so you guys are just as good.
Good luck to all of you and may the best dwarf win!