Hmm…….

On recent stories, Khonshu has managed to absorb the power of the Elder God Set, making him and Moon Knight more powerful:

(Conan: Serpent War issue#4)

Later in the Avengers run, Khonshu had a profecy about Mephisto becoming a major threat and he decided to order Moon Knight to go after the Earth's mightiest heroes in order to steal their powers:

I had to read this entire arc for the sake of this answer, and my point was proven, it feels like an insanely bad Dragon Ball Super storyline. Regardless, I'm forced to use this nonsense.

He stole the powers of:

• Iron Fist:

• Dr. Strange:

• Ghost Rider:

• Thor:

He had the fire of the Immortal dragon of Kun-lun, the sorcery of the sorcerer supreme, a spirit of vengeance, and total control over Mjølnir. He even defeated Mephisto later:

(Avengers(2020)issue#34)

Later, Moon Knight betrayed Khonshu after the God tried to manipulate him into killing Black Panther.

So Moon Knight prayed and became the Fist of Phoenix:

(Avengers(2020)issue#36)

Eventually helping to defeat Khonshu, and even free Thor:

(Yes he lost against Thor, he allowed him to beat him up)

Another possible candidate is Moon Shade:

During the Infinity War event way back in the day, Adam Warlock's malignant counterpart Magnus had created a malignant counterpart for each Marvel hero.

Moon Knight had his, and it was called Moon Shade. Not only he was Moon Knight's evil twin, he had the ability to absorb other living beings, first starting with Franklin Richards' Doppelganger/evil twin:

(Marc Spector: Moon Knight issue#42)

And later he started to absorb other Moon Knights throughout the Marvel multiverse:

(Marc Spector: Moon Knight issue#42)

He is supposedly a multi-dimensional entity, and far more powerful than the Moon Knight we're used to.