This removes all abilities on all cards in all graveyards -- both the ones that matter in a graveyard (dredge, Chronosavant’s ability, etc.) and those that don’t.

If an ability triggers when the object that has it is put into a graveyard from the battlefield, that ability triggers from the battlefield (such as Deadwood Treefolk or Epochrasite, for example), they won’t be affected by Yixlid Jailer.

If an ability triggers when the object that has it is put into a graveyard from anywhere other than the battlefield, that ability triggers from the graveyard, (such as Krosan Tusker, Narcomoeba, or Quagnoth, for example). Yixlid Jailer will prevent those abilities from triggering at all.

If an ability triggers when the object that has it is put into a hidden zone from a graveyard, that ability triggers from the graveyard, (such as Golgari Brownscale), Yixlid Jailer will prevent that ability from triggering.

Some replacement effects cause a card to be put somewhere else instead of being put into a graveyard (such as Legacy Weapon). These effects mean the card is never actually put into the graveyard, so Yixlid Jailer can’t affect it.

Some cards have abilities that modify how they’re put onto the battlefield. For example, Scarwood Treefolk says “Scarwood Treefolk is put onto the battlefield tapped” and Triskelion says “Triskelion enters the battlefield with three +1/+1 counters on it.” Although these cards won’t have these abilities in the graveyard, they will be applied if the cards are put onto the battlefield from the graveyard (due to Zombify, perhaps). What matters is that these cards will have these abilities on the battlefield.

If Mistform Ultimus is in the graveyard, the Ultimus will lose its ability that says “Mistform Ultimus is every creature type,” but it will still *be* all creature types. The way continuous effects work, Mistform Ultimus’s type-changing ability is applied before Yixlid Jailer’s ability removes it.