Need help against Tau and Sisters

Greetings fellow Archons. May your pain never run dry

I am a new addition to the true kin, and as such ask your advice. The adversaries I usually encounter are either Sisters of Battle or Tau (Same person / two armies).

He is a lot more experienced than me and pretty much always beats me. (I normally field our craftworld cousins)
We usually play 1850 point games.

I have presented you with a typical list (From memory) for the two armies. I know they are very different, but instead of making two topics I’ve placed them in the same. You can then respond with advice against the army of your choice ;-)

Fighting the sisters of battle a typical list would be similar to this.

HQ
Inquisitor, Canoness & Priest (no inquisitorial retinue but are often found in the same group surrounded by celestians)

Elite:
Celestian squads.
Callidus Assassin (By every dark muse how I loathe her)

Troops:
4-5 Battlesister squad, often all in rhinos. Every squad equipped with imagifier, flamer and heavy flamer (sometimes a meltagun)

Fast attack:
7 man seraphim unit with inferno pistols
5 man dominion Squad. Armed primarily with storm bolters. Fielded in multimelta immolators

Heavy:
5 man retributor squad with 4 heavy bolters
Exorcist

Fighting the Tau:

HQ:
Shas’o commander with Shas’vre bodyguard. Plasma and missile pods. Shas’o sometimes with cyclic ion blaster

Elite:
3*3 man crisis suits. Plasma and missiles. 2 of these will often deepstrike.

Troops:
6 * 7 man Fire Warriors. (Imagine the sheer amount of S 5 damage this provides)

Fast attack:
Gun drone unit
2 Piranhas with fusion blaster with targeting array

Heavy:
2 broadside suits
2 hammerheads: one with ion cannon. One with railgun. Both with gun drones, decoy launchers and targeting array.

Any advice would be very much appreciated, and I’ll be sure to repay you with fresh slaves from any successful raid…

From what I saw on BoLS Sisters got bitch-slapped. No, really. Nerfed Faith, nerfed Immolators... What's good left? Grey Knights? Wait, they got own codex... Which also isn't so good
Even with point decrese, they wouldn't be good. Ask Ork Boyz.

As for Tau, I think You may use Beasts (to "RAWR!" suits) and flyers (to "nuke" FW).

https://thedarkcity.forummotion.com/t865-a-1500-pt-new-player-who-needs-advice

The above is a link to another thread here where I just did a big write up on strategy for DE in general (focusing on so-called "Venomspam")

I also discuss specific tactics vs. Tau and provide batreps.

Sisters are, at their core, short range Marines.

With that specific list I would list threats as;

Exorcist
Retributers
Rhinos
Everything else

The above list presumes you're running one of the 'conventional' mech spam DE armies - if not your priorities can change.

With Sisters you basic goal (and it shoul dbe easy...depending on your list) is to out shoot the silly little nuns. You have vastly superior range and mobility, so while they're getting their panties in a bunch thinking about how awesome the Emperor's codpiece is, you should be dancing around the edge of their army unleashing a hail of lance and splinter fire.

If you provide your list I can offer more exacting thoughts on both armies - but neither should be particularlt difficult for you. In the grand sense you're operating with a low 1st tier or strong second tier codex, and they're working with third tier stuff.

you should be able to to outshoot the sisters pretty easily. Assault them once weakened,

For Tau, listen to Thor, he knows what he is talking about.

I just posted a story where my Archon (blast pistol, agoniser, ghostplate, shadow field, combat drugs, and one pain token) assaulted three different squads of Fire Warriors over three turns, alone, and killed all of them (winning me the game ).

Sorry if I am just repeating what Thor said about the Tau, but honeslty, assaulting them is the best bet to survival. I have played most of my games against the Tau, and though I don't have any wyches to run, my twenty or so warriors can rip the Tau apart in CC. The biggest problem is getting them there. Praise Khaine for transports.

It would be great to see your list. General. Night shields are a great against Sister and Tau, especially dropping Fire Warrior rapid fire to 6". I also recommend put Dis Cannons on all the radiers. Other than that. It depends on what you are playing with.

My approach to taking Tau is slightly different, in that it is possible for Dark Eldar to out-shoot them with Venom spam.

With your basic MSU Warrior squad in Venom, you have four splinter rifles, a blaster and two splinter cannons. Give the Venom a night shield, and you can sit outside Pulse Rifle range and peck away at them with your cannons. Even without a night shield, you can still do this, but the shield helps against rapid fire and melta weapons anyway, and puts you out of rail rifle and markerlight range and just about anything other than missile pods and railguns.

The intention is to force your opponent to play on your terms. By taking out his Broadsides and Hammerheads early on with your Ravagers and other lances you force his infantry to move up to you in order to be able to shoot at you next turn, which you callously deny by taking advantage of your superior Dark Eldar mobility and moving back to ~30" away from his Fire Warriors. If he drops battlesuits or Kroot on you, focus your fire on them immediately and get them out of the picture while still taking care to stay out of pulse rifle range.

When the time is right, you pounce, usually when you're beginning to run out of maneuvering room because if your opponent is smart, they'll try to corner you, or when you need to start taking objectives. This is when you dart forward and annihilate him in close quarters, because your Warriors are so much better at combat than his, and their numbers have been pretty depleted due to your finagling.

Needless to say, it is quite humbling to Tau players to be beaten at their own game by a nominally assault-oriented army.