ALL HALO ENEMIES SERIES

'Gravemind' had the 'Honor Guard Councilor', a one-off enemy type who appears at the end of the Mausoleum battle.Among their vehicle selection, there is just one Gauss Warthog.

ALL HALO ENEMIES SERIES

'Quarantine Zone' is the only level in the series where you encounter Flood-controlled vehicles, thus also making it the only level where you face off against Scorpions and Warthogs.

According to one of the programmers, it was a rejected concept they forgot to remove.

'Quarantine Zone' has a single Sentinel that shoots with Needler rounds instead of the Sentinel Beam.

They'll probably die when the Flood first appears, and won't follow you to the next half of the level even if they do survive.

'Sacred Icon' contains the only two friendly Jackals in the series.

A trigger kills them if you go around the corner. You can still fight them from across the pit (and grenade-jump across).

The Marines in 'Sacred Icon', who are indirectly encountered.

At the end of the underwater passage on 'Regret', you encounter a group of stealth-cloaked Grunts, which are never seen again (as enemies).

In 'Delta Halo', some Jackals carrying Plasma Rifles are encountered at the second structure.

Despite receiving an entry in the game manual, it is undrivable, only found in this level, and overall acts more as a set piece than an enemy.

In 'Outskirts', you encounter a convoy of Shadows.

These are the only enemy Elites in the game who use human weapons.

As part of the journey to unlock the 'IWHBYD' skull, you face off against seven waves of Elite Ultras, some of whom are using Battle Rifles and SM Gs.

Despite his unique model, he is of absolutely no relevance, has no unique behavior, and no other Marine appears in that state anywhere else. In the first hangar, you encounter the 'Bloody Marine', a Marine that wears less armor than usual and is covered in blood.

'Cairo Station' also has an unusual case of a Unique Ally.

'Cairo Station' has a pair of Elites dual-wielding plasma pistols at the beginning, an uncloaked Stealth Elite, and an Elite wielding both a Plasma Rifle and Needler at the end.

Also in the final level, there is a single Flood Combat Form in the last hallway before the engine room that is allied with the Covenant.

They only appear if you wait around for too long inside the armory. In the final level, 'The Maw' you can encounter the only group of cloaked Flood Combat Forms in the game.This is the only Hunter in the entire game that is not in a pair. Much later in 'Keyes', just before reaching the Captain, a single Hunter will burst out of a side-room to attack a group of Flood.This is the only Combat Form in the game whose extremities are already severed. At the beginning of 'Keyes', a Grunt is chased by a harmless Flood Elite Combat Form whose limbs and head are all missing.They only appear a handful of times in 'Two Betrayals', and nowhere else. These particular enemies also have a unique model in Anniversary, confirming that they are a different entity from standard Grunt Major. 'Two Betrayals' features Grunt Majors using Fuel Rod Guns.His shots are too slow to do any real damage, and he can be left alone or killed with no consequence. In '343 Guilty Spark' you encounter a Marine driven insane by the (then-unencountered) Flood who will slowly shoot at the Chief when approached.

All halo enemies