It definitely isn't bugs or shedim. Hestaby would never have pulled strings to get Horizon into the Tir if it was one of them. Other spirits? Maybe, but unlikely, for the same reasons. The main problem with the Deus is the Consensus theory is that Horizon was around before Crash 2.0. However, Deus could have subverted whatever the initial Consensus was, and substituted himself for it, especially now that no one is looking for him any more.
If Deus had managed to rework his code enough so that people wouldn't recognize him, and, say, approached a megacorp as an entity named Pulsar...