THE
WARP STORM

I played a battle last night against a Chaos Marine player. I noticed halfway through the battle that my Centurions move to slowly to be used as an Attacker. He swarmed them with Chaos Intercessors. What should I do to A. Counter enemies from swarming my Centurions or B. what should I build to support them.

I've split this post off into its own topic, @RZA, so as not to derail @Pharia's.

First off, you should stop your opponent from cheating. No such thing as chaos intercessors
I just found a vid that may be of use

Hoping it should stil be relevant.

Lmao, He kitbashed Intercessors with Chaos Marines to make it seem like they are fallen Primaris

Long time ago... but firstly what chapter are you running?

These are devistator cents? If so then treat em like artillery pieces ie: screen em well ad theyre biggest weakness is melee.... now if you asked if you should use em then I would say no from a competitive standpoint... they are expensive.... VERY expensive for what they're doing... especially with todays terrain and board sizes.... But some chapters can make em work... they rely heavily on either deployment shenanigans or a transport (ofc useing a raider or fly equivalent is pricey especially since they themselves are very pricy...)or good deployment setup and today's setup if your useing a terrain setup from a tournament like system LVO or similar.... (lots of obscuring terrain). + side with them: they are very hard to shift/take out in a shooting contest if they get to stand in light cover. And they pack a heavy punch....
;) Hope it helps :D

Extra: dev.cents are supposed to be siege experts, and they work wonders in a narrative mission set up to attack a bunker/installation/fortress with lots of open fields ;)
Tactical I would gear them probably with grav cannons and try to deep strike em if possible, or transport em to take out elite infantry.... the Las variant can go both ways and needs a reroll Aura to be effective... allso lascannons are very swingy with they're d6 dmg... especially with todays 3d3 days