suppressor or assault rifle

Pfft, when fighting Prometheans I don't use precision weapons. Plasma Pistol and Suppressor are all you need. Crawlers and Crawler Alphas always get close to you and the Crawler Snipers are so rare you can forget about them most of the time and even if they do show up it's not hard to sneak up on them. Just fire a short burst at them from a suppressor to make them flinch and then punch them to death. Crawlers have worse accuracy than Grunts, you won't die if you're methodical about it.

Then you can just Plasma Pistol a Knight's shields away and, little known fact here, you don't need a precision weapon to get a headshot on a knight. Just shoot them twice in the face with any weapon once their shields are down. The first shot opens the helmet, the second shot hits the skull. If for some reason you can't hit their face, a small burst from the suppressor is all you need to soften up an unshielded knight enough that a melee attack will kill them. No need to go wasting the entire mag. Not like it matters since Suppressor effectively has infinite ammo when fighting Prometheans and if you have the Dexterity package the reload time is inconsequential so it effectively never stops shooting. It's even good for Watchers.

Seriously who needs precision weapons for Prometheans? That's for killing Covies and Spartans.
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Is there something about the way I type that makes it sound angry? Maybe it's just something about the way you read.