Besieger Sniper, colloquially known as Heavyweight Sniper, is a branch of the Sniperclass in Arknights.
Besieger Snipers are similar to Deadeye Snipers, but have a range of 3×3 tiles ahead of a minimum range covering 1×3 tiles in front of them with 2-tile extensions to the sides from Elite 1, target enemies with the highest weight over the others when attacking, and have a higher DP cost.
New trait: When attacking a heavy enemy (weight 3 or greater), ATK increased to 115%
Strategies
Besieger Snipers cannot attack enemies in front of them therefore it's advised to have someone block the enemies in a tile ahead of their frontal range, or to deploy them further than other ranged friendly units.
Besieger Sniper's trait will cause occasions where they won't attack the lighter, constantly moving enemies in favor of the idle, heavier enemies. This is especially dangerous if the enemies boast lesser weight and unblockable like Wraiths or Lurkers.
Hencefore, Operators with AOE damage are recommended to help defeating them so that the Snipers can focus on heavier enemies (which is usually more dangerous).
Most heavy enemies have high DEF, which makes the damage output of Besieger Snipers low when against them, although most Besieger Snipers mitigate this by having talents that make their attacks ignore a portion of the target's DEF.
To deal with this, DEF debuffs are recommended to assist in increasing their damage output.
Modules
The SIE-X Module improves the Besieger Sniper's damage output against heavy enemies (which they already prioritizes attacking due to their trait).