From Halopedia, the Halo wiki
Ripa 'Moramee will be automatically deployed as soon as the player finishes their first Temple. If that Arbiter is killed the player can purchase another for 400 resources, but can only have one Arbiter at a time. Ripa uses dual energy swords in battle and cannot attack aircraft unless in rage mode.
When activated, the camera locks onto the Arbiter, whom the player controls with the left thumbstick and attacks with the right. It will use up resources every second it is in use and can be upgraded at the Temple. Rage Mode allows the Arbiter to single out enemy units, lunge at them, and deal damage on them. A fully upgraded Rage increases the player's units' damage while the Rage is still active. This also affects allies, including allied UNSC units, boosting their damage.
Halo Wars 2
Ripa 'Moramee is exclusive to himself and can be built at the War Council. Like other hero units the player is limited to one on the field at a time. Ripa performs well against infantry, vehicles, and structures, but only okay against aircraft. Once the Conduit Incarnate upgrade is purchased Ripa will perform well against aircraft. Ripa can only attack aircraft while using his Rage ability. Unlike his Rage ability in Halo Wars, his Rage in Halo Wars 2 does not allow to player to control him. However, it not longer costs resources to use, and instead lasts for a set time. In Blitz he costs 240 energy and features the Rush ability that eliminates spawn debuffs.