Left for death.
The Abandoned one it was player character of Current / Previous / Other campaigns gone mad; After being left behind by the DM, gained his freedom after breaking the shackles of the beings that made him / she / it "Die".

Memories from the creator.
It doesn't know what are the words that are coastally going through its head.
All spells / actions that this being will cast / use, are replaced by MEMES in general.
It has an unfair amount of chances to parry attacks from one player.
[ After every strike Ranged or Melee with a D20, the player has to roll 15 above to hit]
[ After every saucerful parry the chances of it decay by 2 to a min of 5]
[ If the player getting parried is a range unit, losses his turn]
[ If the player getting parried is a melee unit, breaks his defenses]

Fanatic Revenge
It knows that the gods are mere puppets of a bigger entity out of his reach, it knows it cant hurt it, so might as well hurt his favorite toys.
With any weapon deals [0.5 * + current base damage] against players

Metal Pipe

As a Melee attack: It will try to bash you with it, rolling a D20 to determine if it lands, it can reach 5 feet. In a successful impact it will make the player dizzy, giving him disadvantage in his next attack a -3 in his next roll

Let it fall: It will extend his hand has much as it can and then let the metal pipe fall.
If Caught between 20 feet of it, player will go deaf for 6 turns, if are in the 30 feet away players will a Constitution saving throw DC 14, if already with something in the ears DC 10.
[The Abandoned one is inmune to the effects of the pipe]
[ Hearing it soo much, it has made his brain very smooth]

¿Quieres?

In the middle of the fight it will abruptly stop, like nothing really happened and it will offer you a joint; Can only give one.

Taking it: After taking it, it will ignore the player who took it, but it also will dodge all attacks from it, range, melee, spells, it doesn't care if the player use it.
In case if the player decides to smoke it, just one taste of it and the player will be send to other plane of existence where nothing hurt him and viceversa. The effect last 3 turns.
Once used it will be able to agro set player again.

Slapping it off: Will cause it to enter an enraged state, causing this being to have a turn after every player  in the current cycle, if the cycle is about to end, it will trigger in the next one.

You don't need those.

Blow pancakes with mind: After saying something similar to that, all the party members 25% of their consumable will be gone. Can be stopped, by a Wisdom Saving throw of DC 12 and above.
Cease to be, crushed.
Worst case scenario exploding, Dealing 5 points of damage for every consumable exploding.

F A L L

You Should ### NOW: You serve 0 purpose, all players hearing him say this will fall to their knees; Their guilt will feel like its eating them inside out. Can be snap out of it by a Constitution and Wisdom at the same time, Saving throw above DC10
[dealing 1 points of damage for every turn for 10 turns]
[This its version of Vicious Mockery]

Bells of the past

To the selected target it will rang a bell making him remember bad memories of the past, the target will suffer but no damage will be taken.
The bell will rang 3 times in a row
[ This its version of Taunt]

Thy end is NOW: After parrying 2 attacks in a row, it will propel itself against any ranged or support unit in a 40 feet radius.
if no one but melee are, it will do flying kick towards them making them get flung 30 feet back if light or 10 feet if heavy.
Dealing 8 points of damage + the damage dealt by smashing into a wall that to minimum is 3.
Cannot be avoided.

Uno reverse card: Once per every cycle / round it will reflect any kind of range "action"

Parry: After parrying a player, it will throw D20, below 10 it will say Get Gud or alike. Above 10 it will do a heavy attack, dealing 4 damage + the outcome of a D6.

Counter argument: If told that his habilites are fake or don't exist it will prompt it to say: The source is that i made the F#ck up

During the First Day: It will try to avoid being spotted or to be known, studying the vessel who replaced him.
First Dungeon: It will follow the party, but with slightly hint of them going back to the entrance, it will run away.

Its house: If the players find its house and stole, it will become enraged for the next encounter at the beginning of it.

When reaching half health: It will start using more aggressive Memes

I alone, as all in existence planes, is the Cringe Lord:

Everything will go silent, at it seems to start to dance.
With a flick of his fingers all beings in the room (But it) will take 20 % of their maximum health Damage.
Making every one dizzy, giving disadvantage rolls of -4 in any kind of roll.
Engulfing in flames those caught in its light, dealing 2 points of damage every turn
It does this 3 times.