Manga where a guy has an inter dimensional clown/jester friend

Might be Flame of Recca.

One of the characters, called Joker, dresses like a jester and can create black holes as an attack.

There are also mutated monsters (such as a man turned into a man-lion beast), but those are not created through black holes. Some monsters (zombies, I think) are biological experiments.

The manga Battle Frenzy matches all criteria.

Amidst a disaster, an orphan contracts a sickness.
In his waking hours, he is tormented by his ailment, but when he slumbers, there is infinite darkness.

One day, when he was five years old, a strange Fate Trickster appeared in his dreams. Ten years later, he dreams of becoming a lord. To do so, he takes a chance to trade his fate!

That day, Wang Zhong once again stood at the gates of the Tianjing Heroic Soul Academy. He was about to start a brand new life.

....

An orphan who nearly died when he was 2 years old is cured with the help of the Fate/Destiny Stone and the Playful Clown, Simba grows up to become a battle expert.

As can be read in the webnovel, Simba indeed initially controls the Fate Roulette, which has an effect on Wang Zhong's "soul sea".

Wang Zhong scratched his head. Simba had started that demonic roulette all by himself and aside from the effects it had caused on his soul sea, Simba had shrunk into a palm-sized version of himself. He’d paid a steep cost to forcefully spin the roulette and now lay dormant. If they tried it again, it would likely cost his life. Wang Zhong could only look after himself from now on.

The crack on the seal had widened a bit. Even though his soul power had only risen to 50 grassos, its significance was completely different for Wang Zhong!