From Halopedia, the Halo wiki
Rebel snipers are a type of insurrectionist infantry seen defending rebel-held sites on Harvest and Arcadia. Like regular Rebel Infantry, they wear hoods and a mix of equipment including armour pieces scavenged from UNSC BDUs. They are typically seen in pairs, supporting regular infantry and defending rebel-held sites. They wield an unidentified type of sniper rifle.
In Halo Wars Rebel Snipers can be found in the multiplayer mode, as part of the Insurrectionist faction. Like the insurrectionists, Flood and Sentinels, they are hostile to all players of either team, regardless of UNSC or Covenant affiliation. They serve the rebels as anti-infantry infantry, taking a role akin to the Kig-Yar Snipers available to Covenant players.
Rebel snipers can usually be found alongside a squad of infantry protecting rebel bases, often with one star veterancy. They typically provide support fire for the regular infantry and turrets, and are able to quickly eliminate most infantry, even Spartans. Larger groups of infantry and/ or vehicles, however, are easily capable of overpowering the snipers.
Early in the game, it is beneficial to take out groups of Rebels for the supply crates that appear when they are neutralised. If you are using infantry yourself to fight them, then upgrade some of their features, or bring some vehicle and/or air units along with them.
Also, in addition to upgrading marine features, using large groups of Marines could help take out these infantry killing threats. Take into consideration that the snipers pause to acquire new targets, and use this opportunity to use your main infantry's special ability to take out the snipers for good. Make sure all your units are not focusing on just the snipers, have some units attacking the snipers while others attack Rebel squads, capture structures, or destroy Rebel base turrets.
Air units are also effective at taking out these Rebel snipers. Take a group of Hornets to along to assist your ground forces with the Rebel threats. Scorpions with the Canister Shell upgrade are very effective to take out these snipers usually one shot from the canister from just one should take out both snipers.
List of appearances