What is ff_landslide? It's a firefight map taking place on the landslide area of the level Halo for CE.
You start with 7, 5, or 3 lives (shared between players in coop) on Easy/Normal, Heroic and Legendary difficulty respectively. Lives are displayed in the bottom right corner, and once you lose your last life, you lose.

How:

You fight through 5 rounds, compromised of 7 waves each. Each wave is compromised of 10-30 enemies (approximately), and the makeup of the waves is roughly the same between round (Round 1 Wave 2 has almost the same enemies as Round 2 Wave 2). Enemies are dropped by 2 Spirits, and come from the pathways opposite the spawn area. Waves progress when about 80% of enemies from previous wave are killed, rounds progress when all enemies in previous round are killed. Each Round after the 1st has special attributes:

Round 1 - Normal
Round 2 - Enemies throw more grenades, and always drop grenades upon death (be careful with the flamethrower)
Round 3 - Enemies have more health and shield (between 1.5 and 2 times)
Round 4 - Player has no motion tracker, and invisible enemies are much more common (In CEA graphics only elites are invisible, sorry nothing I can do about this yet)
Round 5 - Combination of the other attributes

You spawn with an AR and a Pistol, both with full ammo, as well as 4 Frag grenades and 2 Plasmas. When you respawn you have an AR and Pistol with 1/2 ammo, and 1 of each grenade type.

If you die holding a weapon, it will DISAPPEAR (I may change this in a future update).

After each round there is a 10 second period before the next starts, this is when weapons, ammo, and healthpacks (and ai ally) are restocked and you have a chance to set up a new defensive position.

Weapons drops are as follows:
AR (420 total rounds)
Rocket Launcher (2 round)
2 Healthpacks
4 Frag grenades
Rocket Ammo
2 Pistol Ammos
3 AR Ammo
3 Shotguns (42 total rounds each)
2 Snipers (1 full ammo, 1 1/2 ammo)