Horus is stated to be infinite and has numerous hax in his arsenal.
Chaos Horus during the events of The End and The Death collapsed all of past, present and future into one 'Isochronal Instant' where all things existed simultaneously, effectively turning the linear timeline into a 'knotted yarn ball' of spacetime. He also surrounded the entire Solar System in a Warp-Storm where the laws of physics no longer applied. The narration also mentions repeatedly how he had the power to destroy entire universes and about fourteen statements where he was called infinite.
During his fight with Sanguinius, Horus was able to move faster than light and also slap Sanguinius with unavoidable attacks along 8th-dimensional space. In the fight between Horus and The Emperor, both fought across thousands of planes of existence simultaneously on physical, spiritual, psychic and symbolical levels. They fought by invoking metaphors that clashed against each other across various realms, in one plane Horus was a fire-breathing dragon and the Emperor an armoured knight, in one the Emperor was a white-dwarf star being devoured by the black hole that was Horus.
There were also moments where they parried each other attacks by sidestepping into adjacent realities, or by dodging attacks across higher dimensional space, or going backwards and forwards in time. They were fighting on Cthonia, Ullanor, Cadia, Ancient Terra, Moloch, etc. simultaneously.
And Horus was holding back throughout the fight which was but a show to try to convince his father to join him. At one point he even lets the Emperor kill him repeatedly for a thousand years straight just to prove that his father doesn't stand a chance against him without ascending into another chaos god. The psychic shockwave of his soul's destruction not only shatters the Warp Storm that had collapsed space and time across the entire solar system, but causes random stars across the rim of the galaxy to spontaneously explode and go supernova.
The higher ends of Warhammer had been getting hyped for decades with statements that had no feats to back them up, but Chaos Horus proved that the hype was true. I would say that he's comfortably above universal but below multiversal.