These two engines work very well together, and both are fairly small engines, allowing for a lot of extra room in the deck for things like handtraps and board breakers. The Horus Engine relys on the new cards debuting in AGOV (Age of Overlord), which center around Pharaonic Sarcophagus , which can send Horus cards from your deck to the GY up to four times per turn, protects Horus monsters you control from card effects that don't target them, and even gives them some battle protection. In addition to this, they also recieved a powerful new Continuous Trap in Canopic Protector, which can summon Horus monsters from your hand or grave multiple times per turn, and is even an easy send for the effect of Sarcophagus or Souls, as it Sets itself back if it was sent from the hand or field to the GY, but banishes itself when it leaves.
This is supplemented by the new monsters they recieved which can all summon themselves from the GY if Sarcophagus is on the field and have secondary effects that proc when a card other than them leaves the field because of your opponent, they consist of Imsety, Glory of Horus, who can search out Sarcophagus and can send a card on the field to the GY with its other effect, as well as Duamutef, Blessing of Horus, which gains ATK/DEF based on how many Horus monsters you control and can draw up to 5 cards depending on how many monsters are in your Main Monster Zones with its other effect, in addition to Hapy, Vanguard of Horus, who can recover cards that are banished or in either player's GY with its second effect, and Qebehsenuef, Aegis of Horus, which prevents your opponent from targeting Horus monsters you control for attacks or with card effects.
The Souls Engine gives us an easy way to add Magicians' Souls to our hand, a powerful card which can send excess spells and traps to the GY for more draws, and if necessary, can even send Imsety to summon itself. It's also an extra body for Link plays, and is a Spellcaster as well, allowing you to make Selene, Queen of the Master Magicians, a strong Link-3 monster which requires a Spellcaster, and can summon a Spellcaster from hand or grave in Defense Position, so no Link monsters, at quick effect speed, and can activate this effect multiple times over the course of a couple of turns based on how many spells are on the field or in the GY when it was Link Summoned.