Are these abilities taught by someone else, other than Ternes?

Blade of Terror
(Paralysis) (1 Round/Assassin, Will)
The appalling viciousness of the Assassin's assault cows the target into submission. The assassin may make a death-attack that causes overwhelming fear to the target of this ability.

Bloodlet
(Level Drain) (supernatural permanent stacks, Fortitude)
The Carotid and Femoral artery are prime targets for a cutting or piercing strike. An accurate slice can cause the most extreme case of profuse bleeding: untreated, such a strike is as good as a death-sentence.

Kneecapper's Knife
(Knockdown) (Rounds/3 Assassin, Reflex)
The legs are a promising, if difficult to hit, target. They are often more lightly armored than the torso, as even the most rigid plate armor has many joints and thin parts in its metal.

Murder
(Death, Death Immunity ignored, Fortitude)
The most valuable and feared tool at the Assassin's disposal is not their famed agility or skill with blade or bow, but their knowledge of anatomy and flagrant disregard for the niceties of honorable combat. This attack leaves nothing about the Assassin's motives to question. A feint, a flash of steel from the shadows, or a careful shot: a strike made with the intent to bring their target down instantly, no matter the cost.

Just keep playing and gaining levels. If not those will not appear.

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"Thou that smelled it thine own self dealt it." - Zorak

You have to be an epic assassin to get all of the skills, yup.

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"Let's unwrite these pages and replace them with our own words."

I believe the assassin widget skills come in at 1 every 2 levels, starting with Braining Blow at level 2 assassin, up to Murder at level 20 assassin.

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Named Most Influential Character, Amia Awards 2011

18 is where it stops.

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Ah, I see! Thanks, guys.