Colossus

Blood of the Colossus. A dead Colossus’s blood can be collected in vials to create 1d10 blood of the colossus potions.

Colossal Stature. Due to its size, the Colossus cannot be pushed or knocked prone by effects that target a creature of Huge size or smaller.

Horror. Any creature that starts its turn within 30 feet of the Colossus must make a DC 13 Wisdom saving throw. On a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the Colossus’s Horror for the next 24 hours.

Mindless. The Colossus cannot take the dash, disengage or dodge action, does not make opportunity attacks and lacks the ability to choose targets freely. When it takes the attack action, roll 1d4: on a 1 or 2, it targets the nearest creature; on a 3 or 4, it targets the last creature that damaged it.

If it cannot see a target, for example as an effect of the darkness or fog cloud spells, the Colossus just assumes it is not there and focuses on visible targets.

Furthermore, the Colossus does not intentionally attack non-Humanoid creatures, but they can still be affected by its area of effect attacks like Slam or Sweep.

Obscure Anatomy. The Colossus is immune to any spell or effect that would alter its shape and size or that would heal it (except for its own Regeneration trait) or revive it. It is also immune to any spell or effect that would instantly kill it, like power word kill but it can be killed by using the wish spell.

In addition, the Colossus's Strength, Dexterity and Constitution scores cannot be increased or reduced, and it is immune to haste and slow spells or spells and features that have similar effects.

Regeneration. The Colossus regains 10 hit points at the start of its turn if it has at least 1 hit point.

In addition, as an action, the Colossus can regain additional 37 (6d8 + 10) hit points.

This trait can also heal Weak Spots (see below). The Colossus instinctively prioritises healing its Throat, and then the Weak Spots that are at 0 hit points. If a Weak Spot regains all lost hit points with this trait, the exceeding hit points are automatically redirected to the second most damaged Weak Spot.

Relentless. If damage reduces the Colossus to 0 Hit Points, it must make a Constitution saving throw with a DC of 5 plus the damage taken. On a successful save, the Colossus drops to 1 Hit Point instead.

Siege Monster. The Colossus’s Slam and Sweep attacks deal double damage to objects and structures.

Weak Spots. The Colossus has several Weak Spots which can be specifically targeted for a variety of effects:

• 2 Ankles (AC 14, 20 hit points, resistance to any damage dealt by ranged attacks): If one Ankle drops to 0 hit points, the Colossus falls on one knee (making its Eyes, Jaw and Throat targetable without climbing its body; see below) and its walking speed drops to 0 feet until the same Ankle regains 1 hit point. If both Ankles are at 0 hit points at the same time, the Colossus fall prone and cannot get up until at least one Ankle regains 1 hit point.
• 2 Eyes (AC 16, 10 hit points, resistance to any damage dealt by ranged attacks): If one Eye drops to 0 hit points, the Colossus has disadvantage on attack rolls and Wisdom (Perception) checks until the same Eye regains 1 hit point. If both Eyes are at 0 hit points at the same time, the Colossus is blinded until at least one Eye regains 1 hit point (this is the only way to blind the Colossus). To target the Eyes with a melee attack, any non-flying creature of Large size or smaller must use an action to make a successful DC 14 Strength (Athletics) or Dexterity (Acrobatics) check to climb the Colossus’s body and get within reach of the Eyes.
• 2 Wrists (AC 14, 20 hit points, resistance to any damage dealt by ranged attacks): If one Wrist drops to 0 hit points, the Colossus can’t take the Sweep action until the same Wrist regains 1 hit point. If both Wrists are at 0 hit points at the same time, the Colossus can’t take the Slam action until at least one Wrist regains 1 hit point.
• Belly (AC 12, 30 hit points, resistance to any damage dealt by ranged attacks): If the Belly drops to 0 hit points, all creatures previously swallowed through the Swallow action (see below) fall prone in a random unoccupied space within 5 feet of the Colossus and are no longer incapacitated. Until the Belly regains 1 hit point, the Colossus can’t use its Swallow action.
• Jaw (AC 16, 20 hit points, resistance to any damage dealt by ranged attacks): If the Jaw drops to 0 hit points, the Colossus can’t take the Bite action or the Maw of Hopelessness reaction until the Jaw regains 1 hit point. In addition, if the Colossus was grappling a creature with its Bite, the creature is no longer grappled. To target the Jaw with a melee attack, any non-flying creature of Large size or smaller must use an action to make a successful DC 14 Strength (Athletics) or Dexterity (Acrobatics) check to climb the Colossus’s body and get within reach of the Jaw.
• Throat (AC 22, 50 hit points, immunity to any damage dealt by ranged attacks): If the Throat drops to 0 hit points, the Colossus dies. To target the Throat with a melee attack, any non-flying creature of Large size or smaller must use an action to make a successful DC 14 Strength (Athletics) or Dexterity (Acrobatics) check to climb the Colossus’s body and get within reach of the Throat.

All Weak Spots must specifically be targeted by an attack: they automatically succeed on Dexterity saving throws to avoid damage, taking none even when they would take half. 

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 46 (8d8 + 10) piercing damage. If the target is a Large or smaller creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Colossus can’t bite another target.

Slam. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 37 (6d8 + 10) bludgeoning damage, and the target must make a DC 20 Dexterity saving throw or be knocked prone. Even if the Slam attack misses, any creature that stands within 5 feet of the target must make a DC 14 Dexterity saving throw or take 23 (3d8 + 10) bludgeoning damage and be knocked prone.

Swallow. The Colossus swallows a Large or smaller creature it is grappling with its Bite. While swallowed, the creature is incapacitated, has total cover against attacks and other effects outside the Colossus, and takes 27 (6d8) necrotic damage at the start of each of the Colossus’s turns. The Colossus regains an amount of hit points equal to half the necrotic damage dealt (which can be used to heal a specific Weak Spot). If a creature drops to 0 hit points while swallowed, it dies instantly.

If the Colossus dies, a swallowed creature is no longer incapacitated.

Sweep. The Colossus swings its massive arm in a wide arc, crushing everything in its way. This attack affects all creatures in a 20-foot cone extending from the Colossus. Each creature in that area must make a DC 14 Dexterity saving throw. On a failed save, a creature takes 46 (8d8 + 10) bludgeoning damage and is pushed 20 feet away from the Colossus. On a successful save, a creature takes half as much damage and is not pushed.

For unknown reasons, as if it was instructed to do so, the Colossus can only take the Sweep action once every three rounds.

Maw of Hopelessness. The Colossus exhibits a paradoxical survival instinct when it comes to protect its foremost vulnerability. When a creature makes a melee attack against its Throat, the Colossus can use its Bite action on the attacker (the reaction is resolved before the triggering attack can deal damage).

This reaction can be prevented only by destroying its Jaw (see above).