Scutarius

Scutarii are slayer creatures, requiring 81 Slayer to kill. Described as a 'shielder', it is a member of the Order of Ascension.

These monsters are found in the Monastery of Ascension, located northeast of Mobilising armies in the Feldip Hills along with Gladii, Capsarii and Rorarii.

Tips
Any damage dealt to this monster from the front or sides is massively reduced by 90%. In order to deal full damage, they must be hit from the back.

As a solo player, one approach is to use Binding Shot or Tight Bindings to hold it in place, and then run behind it and attack. This is slow and somewhat difficult, but better than frontal attacks.

Multiple-target abilities are inherently risky, as these monsters are usually close to other Scutarii. Their defensive abilities can make attacks involving more than one of them a problem for players. With that said, Shots ricocheted off other enemies that manage to hit Scutarii in the back will deal 20% bonus damage. Once adrenaline is high enough for threshold abilities, Bombardment is also useful because it hits this monster for normal damage, regardless of where the player is standing. Just be careful of collateral damage.

Note that Scutarii are extremely hard on combat familiars, including most Beast of Burden familiars. Even a war tortoise won't last long enough to be useful. High level titans can be useful, but if you don't want to expend them, teams going after these monsters might consider non-combat familiars like the Bunyip and Unicorn stallion.

Trivia

 * This monster's name comes from the Latin word for 'shield-bearer', bearing similarities to this monster's appearance.
 * This monster and the other monsters in the dungeon are the first to have a weakness to a generic attack style (in this case, Ranged). These weaknesses were previously restricted to players.
 * If stunned, Scutarii are still able to attack a player even though they do not turn around, making it look as if it was attacking at the air.
 * Despite the damage reduction, if Scutarii are attacked from the front but the player moves behind just as their ability hits them, it will deal full damage instead of reduced damage. It is unknown whether it is a glitch or not. Bombardment will never deal reduced damage.
 * If a Scutarius is stunned, and then the stun effect is off, even if the player is under the Scutarius, it will not move from the spot it was stunned in. It might be an oversight or glitch from Jagex.