Cataclysmic Rhythm is a unique Sacred Gear, which falls under the category of Metal Arms. Cataclysmic Rhythm is a Longinus-tier Sacred Gear with the spirit of Alintor, the so called "God of Destruction" in the Realm of Metal.

The most basic ability of Cataclysmic Rhytm is increasing the host's physical abilities, which get stronger through training. The host of Cataclysmic Rhythm has access to Alintor's army of metal-crazed zombie peasants called Moshers. Moshers are basic foot soldiers who are....rather dimwitted fellows. They're capable of following basic commands and are amazing in large numbers, sort of like Rats or Goblins. Moshers appear as faceless humans, both male and female, with clothes befitting of metal heads with some having hair. Y/N summons Moshers in small but large numbers because when they're bored or have nothing to kill, they go on a rampage and turn anything into a mosh pit.

Y/N currently has a single special Mosher known as a Fallen Mosher. It looks like a regular one, but it has black wings and can use light weapons. His current and only one can use green light weapons. 

Cataclysmic Rhythm's flagship ability, however, is its use of monster spirits to forge weapons, which are based on what the host uses as a conduit at that given moment. Y/N uses his guitar, which takes the base form of an axe mixed with an electric guitar.

Stygian Tristitia

Stygian Tristitia is made from the body of a variant of the beast Zinogre called Stygian Zinogre. This guitar grants Y/N the ability to manipulate Red Lightning, which is known to be a very violent form of lightning. Stygian Tristitia's lightning also harms dragons like Dragon-slaying swords.

Devil's Lute

Devil's Lute is made from the body of a variant of beast Magnamalo called Scorned Magnamalo. This guitar grants Y/N the ability to manipulate a material known as Hellfire. Contrary to popular to belief, Magnamalo's Hellfire is an explosive purple gas that easily catches a light. 

Ruinous Desolation

Ruinous Desolation is made from the body of the Ruiner Nergigante, a legendary dragon said to have been tempered by the scars of countless battles. This guitar functions more like a melee weapon being rather heavy, but its true ability is shooting a multitude of spikes. These spikes grow back at a fast rate and the darker they become, the stronger they are....is the usual case. The spikes from a Ruiner Nergigante, and Ruinous Desolation by extension, are metallic in nature and even stronger than normal

He'll have 15 Hunting Horns in total. I recommend suggesting a monster you like and I'll look into their Hunting Horn. If they're too similar in abilities, like Lightenna and Diorekkusu both being Thunder monsters, or don't really have much of an ability, like Grimclaw Tigrex, then I won't add it. Not trying to be an asshole or anything, but I know everyone likes variety