From Halopedia, the Halo wiki
Pegasus is a Halo 5: Guardians multiplayer map created from the Forge map Alpine. It was featured in the Halo 5: Guardians Multiplayer Beta. This asymmetrical, roughly square map features long, open sight-lines and sloped pathways, and is suited for 4v4 players, whether FFA or Team matches. The map features the new rocket launcher and the sniper rifle as power weapons.
The map itself is an ONI simulation provided to Spartan-IVs for familiarization with strange structures that appeared on the surface of Delta Halo. Tactical exercises conducted on Pegasus and Orion would precede a Spartan investigation on the ring.