I fielded it twice so far, both times combined with Cegorach's Jest and DE allies.
In the first game, it got utterly destroyed. I played against GK and made a lot of mistakes early on.
The second game was against DA (Green Wing), was a close game, and the formation performed somewhat better.
A few things that I noticed:
- Death Jesters are relatively cheap objective holders, but don't put out much pain (he never inflicted a wound in the 3 turns he lived)
- Shadowseers are rather good melee units, but he should never charge a nearly full tac squad on his own. Yes, it's somewhat clear, but it was at the end of the game and I had no chance to win so I just wanted to see how he 'could' perform in melee.
- Phantasmancy is good, but useless for the Formation if you roll the nova and the witchfire with many attackdice (don't have the book on me, but powers 2 and 3)
- The solitaire can really wreck vehicles with his auto-glances and many attacks. The main thing with him is, keep him hidden until turn 2 at least. He really doesn't want to charge a gunline.
- Infiltration is boss with those 3 guys. I hold just after deployment 4 maelstorm objectives while 2 out of 3 were completely hidden and the deathjester had a 2+ cover.
- Don't count on your 2+ cover, ever! My death jester died to 4 bolter wounds after covering half of his army for one turn.
Conclusion:
Easiest way to get a solitaire, who is awesome when supported.
Shadowseer is definetely a supporting character. Probably better to roll on telepathy for that infiltrating psychic shriek (with -2LD). His own table is to unreliable for a single char.
Deathjester looks good on paper, but is only a distraction without ablative wounds.
Omega