The Serpent of shuriken was originally a copy of Tau's Fish of fury, and revolved around shooting under their transports, to not give away coversaves to the opponent while gaining cover saves themselves, with the Dire Avenger shrine and battle focus the Avengers can just move back and forth behind their transport instead of shooting under it.
Here is how it could be employed:
10x Dire Avengers, Exarch
+ Wave serpent, shuriken cannon.
10x Dire Avengers
+ Wave serpent, shuriken cannon.
10x Dire Avengers
+ Wave serpent, shuriken cannon.
790p
The idea is to go second, and first turn all serpents will jink from any incoming fire since you will likely be moving the serpent flat-out into position. The serpents then need to survive without jinking turn 2, if they do, they will be able to release a powerful beta strike, by moving the serpents only 6" you can both release the Avengers and fire all 3 guns. The avengers can then also use their ability to fire extra shots. Combined this would results in 18+6D6 ~= 39 S6 shots, 9 of them twin-linked. so 28 hits. That's 3.11 HP on 3 AV11 vehicles, statistically.
The Avengers then provides another 90 S4 shots. (not counting the exarch's higher BS) this is 75 hits.
That's a dead 50 man blob of guardsmen,22 MEQ or 12.5 TEQ.
A similar thing can be done by using a falcon cloud strike formation like this:
6x Dire Avengers, Exarch
+Falcon, lance.
6x Dire Avengers
+Falcon, lance.
6x Dire Avengers
+Falcon, lance.
634p
That's 6 S8 hits that penetrates all normal armour and has potential to explode vehicles.
And the Avengers will put out 45 hits (not counting the exarch's higher BS), that's 30 Guardmen in bodybags. The cons with the falcon cloudstrike is that the falcons need to be rolled for, and they can't split fire. However they can be guided, sticking a farseer in there with guide and prescience may make it even better.
Thoughts?