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I got my wraithguard really cheap and I've painted them quite well, they've done really poor in games but I would be shame not to use them. Think the list is ok? or are wraithguard too much of a drawback? They seemed to work better when I had had 3 wraithlords.
8+1 Banshees w/Exarch w/executioner, war shout(moral test or ws1, acrobatic(counter-attack)
Transport: wave serpent w/rocket launchers, shuriken cannon, spirit stones 316
10 Wraithguard w/Warlock w/conceal 390
8+1 Dire Avengers w/Exach w/shimmershield, bladestorm, defend 165
5 Path finders
5 Path finders
Mind if I ask why they have not done well? This would make it possible to make suggestions based on that as well as the list.
As for the list my first and biggest problem is no fortune for your wraithguard. They cost so much that I try to protect them as much as possible, rerolling the saves after the enemy has managed to wound t6 makes them alot harder to kill off. The Banshees can work for your counter charge unit but I worry that with only 3 tanks their ride might get dropped early on also without doom they can struggle to get kills. Fire prisms can work well with the templates thinning out hordes so no problem with them being included but I also see wraithlords working well in the list.
Possible changes would be to drop a troop choice, one of the ranger squads seems the best choice to me. With the points I would recommend getting a wraithlord built for AT, the chance to damage or at least shake a tank while your force is closing will be very helpful also with a brightlance and EML it can wound infantry easy and instant death most targets ( nobs come to mind ). Maybe dropping the banshees and waveserpent for a harlie troupe with a shadowseer. It will actually be cheaper than the banshees and transport combined, with VoT they can foot slog along with the wraithguard and be fairly safe until the enemy closes. With extra points pick up a farseer with fortune, runes of witnessing might be worth the cost as it would make it more likely that you will not have to face a round without fortune.
Those would be the general changes I think would help the list, hope I gave you some food for thought.