How to learn all 3 Unforgivable Curses

All three Unforgivable Curses are tied to Sebastian Sallow's quest chain — they're not regular spells you find. You learn them at specific moments.

The order

Crucio — In the Shadow of the Study (Sebastian's first major personal quest, level ~13).
- Sebastian asks if you want to learn it. Pick "Show me" to learn. Refusing locks all three.
Imperio — In the Shadow of the Relic (Sebastian quest, level ~17-19).
- Cast Crucio on a target during the questline mission. Sebastian then teaches Imperio at the end.
Avada Kedavra — In the Shadow of the Study (Sebastian's late quest, level ~22-25).
- Sebastian teaches it directly. NO further quest gates.

Important caveats

You cannot learn AK without Crucio first. The chain order is hard-locked.
Once learned, Unforgivables are permanent for that save — they appear in the Spells menu.
Casting them in front of Hogwarts staff does NOT trigger consequences. Hogwarts Legacy doesn't track "witnesses" for these spells, despite the lore.

Combat use

Crucio is great for tough enemies — the DoT stacks.
Imperio turns one enemy into your ally for ~10 seconds. Spam it on the strongest target in a fight.
Avada Kedavra instakills any non-boss target. Long cooldown unless you grab the talent.

Trophies

The Cruciatus Curse — cast Crucio.
The Imperius Curse — cast Imperio.
The Killing Curse — cast AK.
The Unforgivable — cast all three.

If stuck: if Sebastian doesn't progress past Crucio teaching, you may have a side-quest gate. Talk to Ominis Gaunt in the Slytherin common room — he sometimes triggers the next chain entry.