Baelor

See the Monster Manual (p. 82) for the following two traits:

Avoidance. If the displacer beast is subjected to an effect that allows it to make a saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Displacement. The displacer beast projects a magical illusion that makes it appear to be standing near its actual location, causing attack rolls against it to have disadvantage. If it is hit by an attack, this trait is disrupted until the end of its next turn. This trait is also disrupted while the displacer beast is incapacitated or has a speed of 0.

Darkvision 60 ft.

Speed 40 ft.

Multiattack. The displacer beast makes two attacks with its tentacles.

Tentacle. Melee Weapon Attack: +4 to hit, reach 10ft., one target. Hit: 6 (ld6 + 3) bludgeoning damage plus 3 (1d6) piercing damage.

Opportunity Attack. If an enemy walks within a 10ft cone in front of Baelor, he may use his Reaction to attack that enemy if they are not targeting Baelor.

Leveling System:

For every 3-5 PC levels that Baelor's master gains, Baelor gains a new Action or Special Trait as determined by the DM that would fit well with the playstyle that Baelor has been using and developing. Additionally, once Baelor's master reaches level 5, Baelor grows to become a large creature (a full grown Displacer Beast) capable of being mounted with the right kind of saddle. Price and/or necessary materials may be determined by the DM for how to make the saddle, but should be double or triple the standard prices of a normal saddle due to the irregularities of a Displacer Beast's body compared to traditional mounts.

Actions and/or Traits that can be learned/granted may include (but are not limited to):

Invisibility

An Ability Point (or two)

Extra 1d6 damage dice to each Tentacle attack.

Tail Whip: (2d4 + DEX; +3 to hit)

Claw: (1d12 + STR: +5 to hit; range 5 ft.) Baelor may use his Claw attack in tandem with his tentacle attack if they are attacking the same person (doesn't matter if it's with the first tentacle attack, the second, or both).

Shadowfang Bite: (1d10 + STR, +4 to hit; range 5 ft). On a successful hit, creature must roll a DC 13 Constitution saving throw. On a failed save, target creature takes 4d6 Shadow damage. If target creature saves, it takes half damage (except on a critical save, then it takes no damage).

Shadowmist Teleport: Baelor may teleport in any direction (including up onto a ledge or down below) up to 20 ft away. Upon doing so, Baelor leaves behind a 10ft shadowmist sphere that both magically and physically obscures vision and line of sight of friend and foe that are caught within the mist. For all other creatures standing outside of the mist, only their line of sight is obscured by normal physical means.

Surprise Attack: When attacking from stealth or from invisibility, Baelor's next Multiattack or other chosen attack method has advantage.

Resistant to Shadow Damage

Terrifying Presence (Baelor's master must be lvl 10 or greater): Target creature must roll two Charisma Saving Throws of 11 + [Baelor's CHA modifier] to save otherwise they will experience one of the two following effects:

A. If 2 saving throw failures:  target creature is terrified and will attempt to flee combat if it can or will fight with disadvantage on every roll for 1 minute (or a minimum of three turns as determined by the DM).

B. If 1 saving throw failure: target creature rolls with disadvantage on its next attack. 

Terrifying Aura (Passive) (Baelor's master must be lvl 15 or greater): All enemy creatures within 60 ft of Baelor must roll a DC 11 Charisma saving throw or be terrified of Baelor for the rest of their miserable lives. If terrified, creature(s) will attempt to run away in fear and will everything they can not to confront Baelor (at least not head on).