Ok ladies and gents I had an idea for my gaming group for acension and I need your help...

I was planning on using death watch stats for tyranids (only using a few not the whole caboodle). The most powerful one they will be facing is the Brood lord from Mark of xenos.

First thing reasonable PT for tyranid powers. The reason why I am asking is because I want to use their psyker powers to keep to the true feel of the race. I am also keeping their stats to drive home the brutal nature of the universe (the reason why is because it seams semi realistice to me). Anyway I wold like help converting the tyranids psychic powers if anyone is willing to help.

Second of all this is taking place on a space hulk and this mission will be the finally and kind of a kicker. I was planning to have a mass battle play out between Chaos forces and a genestealer cult (Murder mayham as i like to call it) basically there is going to be two boss fights but meh. Not only will they stop a Heretic from acending but a potential tyranid invasion as well. I would like your imput and may helpful tips on encounters

Lastly I was thinking of giving them assistance with a deathwatch npc or some such number of people to assist them to make the mission important and drive home the fact its all or nothing. So in short any ideas on helpful npcs that would assist them.

Hey, I made stats for Tyranids for Dark Heresy, although they are neither playtested or really finished they did cover the psyker powers...

mind you these are the ones from the board game, not neccesarily what you are looking for, though i hope they help

and here they are:

Broodlord:
Commanding gaze : 1/2 action, threshold 11, range Sight, Opposed WP test to target, if the broodlord wins the target may only make a 1/2 aciton next turn and may not make any attacking actions against any target. overbleed by 10 allows the broodlord to affect another target within 5 sq of the original target.
touch of madness

Hive Tyrant:
psychic crush (malice grip), Warp howl, Inflict pain and healer mixed (deals 1d10 levels of fatiuge and heals the tyrant for that much hp) (leech essense), Compel, Sense Presence, Broodlords Commanding gaze (paroxyism)

Tervigon:
Catalyst: thrshold 16, focus 1/2 action, sustained, range 10m, grants target regen trait, overbleed 5, affect another target
onslaught: threshold 19, focus 1/2 action, sustained range 10m, gives target hip shooting and frenzy as a free action as long as sustained
healer and seal wounds

and thats all the psyker, although the zoanthrope has a psychic lance, I counted it as a gun as the zoanthrope is built to not truly evoke psychich phenomena...

with the following stats, using WP not balistic, also rolls one dice, on a 9 triggers phenomena
Warp Blast(140m S/-/-, 1d10+8 E, Pen 2, Blast 4)

Warp Lance (200m, S/-/-, 2d10+14 E, Pen 4 )

hope this helps.. In case you need justification to use less than all the beasties just say that it is a surviving hive fleet that is on planet and cannot aford to use biomass to create new creatures