Wave Traits

The wave traits page allows you to edit the traits for NPCs. Note that these traits are far less varied than player traits, and mainly concern AI behavior.

The fields available to edit are as follows:

Damage Modifier
Scales the amount of damage that NPC weapons and melees do.
Damage Resistance
Scales the amount of damage that NPCs can withstand. Note that this also scales the strength of breakable enemy armor, such as Grunt Ultras' helmets.
Vision

Controls how likely an NPC is to notice an enemy within its line of sight.

The "Nearsighted" option reduces an NPC's sight range to 20% and reduces their field of view (i.e. vision cone angle) to 80%. The "Eagle Eye" option boosts their sight range to 150% and their field of view to 120%.

Hearing
Controls how likely an NPC is to notice enemies that are making noise. The "Sharp" option doubles the NPC's hearing range.
Luck

Controls how likely an NPC is to dodge grenades and needles, versus how likely an NPC Grunt is to flee or attempt a suicide bombing.

Unlucky
Never evades fire, dives away from grenades, or attempts a suicide bombing. Always retreats after diving. Never goes berserk after shields pop. Leaders don't go berserk after their followers are all killed.
Normal
No changes are made to the base AI data.
Lucky
75% more likely to evade fire and dive away from grenades. Never retreats after diving. The delays between successive melee attacks, and successive grenade throws, are halved. Twice as likely to melee.
Leprechaun
Evades fire and dives away from grenades as often as is physically possible. Never retreats after diving. Always attempts a suicide bombing when "broken." Always retreats when their leader dies. Always goes berserk when their shields pop. Leaders always go berserk when their followers are all killed. The delays between successive melee attacks, and successive grenade throws, are halved. Always melees when it is possible to do so.
Shootiness

Controls NPCs' accuracy and tendency to fire excess shots.

Grenades
Controls how often NPCs use grenades. The "Catch" option significantly increases the NPC's likelihood of throwing grenades, halves the delay between successive grenade throws, and doubles grenades' outbound velocity.
Don't Drop Equipment on Death
If this option is enabled, then NPCs will not drop weapons or grenades when they die.
Assassination Immunity
Controls whether NPCs are immune to instant-kill melees to the back, and to special finishing moves (which players will not be allowed to perform).
Headshot Immunity
Controls whether NPCs are immune to instant-kill headshots.

All exact stats for AI changes are based on examination of the game data using the Halo: Reach Editing Kit. Not all behaviors (e.g. "going berserk") may apply to all NPC types.

Under the hood

The effects of the Vision, Hearing, Luck, and Grenades options are all defined in the globals\ai_globals.ai_globals tag.

The effects of the Shootiness option appear to be defined on character tags. The tags/ai/generic.character tag defines defaults that can be overridden by each individual NPC type. Within a character tag, "firing patterns" (with the same names as the Shootiness option values) can be defined per weapon, and the parameters associated with a firing pattern include: