A difficulty changes the number, type, and vitality of enemies in a Campaign mode. There are four difficulty ratings in the first person shooter Halo games: Easy, Normal, Heroic, and Legendary, from the easiest to hardest. LASO, a fan-made difficulty, requires players to turn on all skulls while playing on Legendary.
Halo Wars is a special case, at higher difficulties resource gather rates are increased along with the usual health, armor and intelligence bonuses. It also has a fifth difficulty level: Automatic (40). It begins at a rating of 40 and increases based on victories, a rating of 40 is similar to the Easy difficulty setting. One of 60 is Normal, 80 Heroic and 100 is Legendary. Where this difficulty differs is that the rating can increase above 100, up to a maximum of 199, essentially keeping pace with the players skill level and always providing a challenge. However the rating can increase based on the outcome of team games as well. Frequent team games can cause the rating to exceed the players 1v1 skill level making victory only possible in 2v2 or 3v3 games where allies can distract the enemy. In some cutscenes in the Halo games, different difficulties can change the dialogue you hear, often more rude or confident as difficulty increases; for example in the cutscene level "Arrival " in Halo 3, Johnson's last line changes with every difficulty.
Each difficulty has a different symbol. Most of the achievements in the Halo series do not unlock when played on Easy, as most need to be on Normal or higher, although there are exceptions (most notably Halo Wars). The Gamerpoints earned are as follows:
- Campaign Complete: Normal (125 )
- Campaign Complete: Heroic (125 )
- Campaign Complete: Legendary (125 )
Halo 3: ODST
- Campaign Complete: Normal (100 )
- Campaign Complete: Heroic (100 )
- Campaign Complete: Legendary (100 )
- The Soldier we needed you to be (25 )
- Folks Need Heroes... (50 )
- Gods Must Be Strong (125 )
- A Monument to All Your Sins (150 )
- Big Al's Scooter (10 , Heroic)
- Penny Pincher (10 , Heroic)
- Adjudicate the Arbiter (30 , Heroic)
- Mr. Punctual (15 , Heroic)
- Detour The Great Journey (50 , Legendary)
The Marathon symbol can be clearly seen on the Easy shield, which is bare. The Normal shield has a Combat knife set diagonally across it, while the Heroic shield has two Combat Knives on it, crossing over each other to make an X shape. The Legendary shield also has the Combat Knives on it, with a Sangheili skull upon those, a crack in the upper right hand corner of the skull.
This differs in Halo 3: ODST. Instead of Combat Knives, there are Suppressed SMG's (the signature weapon for ODST's protagonist), and the Sangheili skull is replaced with a human skull.
In Halo Wars the difficulty settings do not have icons.