The Abnormal tier is split into two sub-tiers: Combat Abnormal and Utility Abnormal.
Combat Abnormal Mobs
Despite Bairns, Scampers, and Gastgebers being classified as Combat Abnormal, their entity class actually extends them to the Infected and Evolved tiers respectively (Bairns as Infected and Scampers and Gastgebers as Evolved).
Shared Aspects & Capabilities
Abnormal are hostile (excluding Gastgebers) to most non-Spore mobs, with the exceptions being Animals and Fish (unless Should attack Animals is enabled via the Config) and mobs included in the Mobs Not Targeted blacklist within the Config.
Can perform short dashes in liquids to pursue a target.
Able to utilize Kill Points to grant themselves buffs (excluding Infested Constructs).
Present a weakness to the cold.
Will despawn during Proto World Modifier if they are at least 256 blocks away from a player (excluding Bairns, Scampers, and Gastgebers).
Are not affected by Vanilla Despawning (excluding Bairns without Evolution Points).
In regards to Frostbite, have a Body Heat of 4 and Enum Percentage of 5% (excluding Bairns, Scampers, and Gastgebers).
Utility Abnormal Mobs
The Mobs listed in this tier (Hallucination, Scent, and Challenge Watcher) are the major Utility Abnormal and are generally independent from other Mobs. However, there are many more Spore entities that are classified as Utility Abnormal, but are heavily dependent on other Mobs. This includes Evoker Claws, Hexenmeister Claws, Tendrils, Waves, Dismembered Corpses, Nukes, Hohlfresser Segments, Leviathan Segments, and Tumoroid Nukes. Tentacles are also considered as Utility Abnormal but aren't listed for their own reasons.
Shared Aspects & Capabilities
Are affected by Vanilla Despawning (excluding Tendrils, Hohlfresser Segments, and Leviathan Segments).
Trivia
The Abnormal tier is also called 'Unknown' and 'Anomalies' due to the nature of the Mobs.