Looks like it can roll either 1 or 2 skills.
https://tsw.vn.cz/quests/Sometimes you can find where it changed by looking at past documentation updates.
Median XL Σ 1.4.0https://docs.median-xl.com/Median XL Σ 1.3.0https://www.median-xl.com/version/sigma-1-3-0.phpMedian XL Σ 1.2.0https://www.median-xl.com/version/sigma-1-2-0.phpMedian XL Σ 1.1.0https://www.median-xl.com/version/sigma-1-1-0.phpNEPHALEM'S SACRIFICE
ULDYSSIAN:
Is no longer a purify boss
Rebalanced all stats, changed AI, now has an overlay
Has Soulsteal (25k health on player kill)
Now teleports
EDYREMS: increased speed, fire damage, health and AR. Reduced damage, and they are now CB immune
Removed proc from
charm due to interference with monster AI, can now roll an extra skill instead. Increased edyrem buff
Rebalanced experience on all stages
Median XL Σ 1.0.0https://www.median-xl.com/version/sigma-1-0-0.phpNEPHALEM'S SACRIFICE
Charm now gives a bonus to Edyrem life and has a minimum roll of +1 to All Skills. Now called the Neutrality Pact. Reanimate removed from charm. Now has a Purify oSkill instead of charges