Hey Fellow Gm's back from along hiatus I am currently developing a only war campaign for a local group and was interested in the idea of bringing enemies over from other sources and tweaking them for only war.

the enemies I want my players to encounter are Rak'gol, Tau, Orks and chaos/traitor armies with maybe either Tyranids or Necrons making a later appearance and have the dark elder come in for real space raids every now and then.

Any tips on brings some of the enemies I listed over with a few tweaks and adjustments?

Necrons you don't need to tweak at all, since there are versions written already for Black Crusade, which is a 99.99% identical game system. Orks and chaos and dark eldar stuff have already been written up in OW.

Necrons will slaughter Only War characters though, so I don't recommend using them unless the characters are in a tank.

I have played an Only War game against necron warriors - with the players dug in behind good cover, with comrades and above all heavy weapons, they can hold necron warriors off.

For a bit.

Immortals, on the other hand, will murder them very quickly.

Immortals are effectively space marines that regenerate.

Yeah.

Out of curiosity, did your necrons have the reanimation protocols rule from Hand of Corruption, or just regeneration?

Ah well necrons seem like abit of a stretch hmmm I might switch it to chaos then Since I am building a word bearers Npc using black crusade to lead some chaos marines and a couple traitor regiments.

We haven't started playing yet I am just more or less setting up the enemies in question.

Not sure if it is relevant, but I figure I'll mention it. In one thread some time ago, someone mentioned the "differences" between an OW CSM, thinking it was a Dark Apostle, and his BC counterpart; they seemed to think that the OW one spanked BC's, even though BC is made to use Space Marines, while OW is only really intending to mention them, and MAYBE make your Guardsmen fight CSM, occasionally. While I suppose there aren't clear-cut rules in Enemies of the Imperium for making such things, you might want to look at them, if you have access, for a baseline. Best of luck; Word Bearers are fun

BC CSMs are meant to play alongside human characters, so starting ones are somewhat toned down (though still killing machines).

Can Anyone help with Tyranid Profile conversions? id like to introduce them to my games Aswell as Tau