Elden Ring: 10 Secret Stories & Locations You NEED To Find
3. The Omen Twins And Their Shackles
In order to defeat the Omen Twins, Morgott and Mohg, one may make use of their "shackles", which are items that immobilise them temporarily in battle.
These can be especially useful given both Mohg and Morgott (or Margit, as he's known in your first two encounters) are Demigod bosses, and can be a particular challenge to take down.
Another seemingly unintended side-effect of these shackles are that you can use them to dispel nearby illusory walls, trigger some dungeon traps - including the fire pillar trap within the Auriza Hero's Grave, allowing the three chariots in the dungeon to collide with each other. It's important to note that Margit's Shackle has a wider range than Mohg's.
From a lore perspective, finding these shackles reveal a lot about the sad history behind the twins's childhood. Imprisoned in the subterranean Shunning Grounds, shackled by Golden Order magic, even though they were Marika's own children - it's a wonder Morgott was still so loyal to the Greater Will, in contrast with Mohg's full, blood-soaked rebellion.
It's unknown if they were imprisoned together, but Mohg's shackle being soaked in blood gives an inkling as to how he escaped it in the first place.