She must be destroyed in a battle and not by an effect for the discard effect to work. In addition, the "once a turn" clause at the start is for if she is the MC, since otherwise, it could feasibly activate multiple times in a turn.
Nyx: Cursed Shaman
Class
Dark Mage ({{{class_type}}})
Cost
2
Symbol
Affinities
Attack
50
Support
20
Range
1-2
Quote
Skill 1
{{{skill1}}}
Skill 2
{{{skill2}}}
Support Skill
N/A
Card Code
{{{card_code}}}
Illustrator
Comment
Nyx: Forbidden Dark Mage
Class
Dark Mage ({{{class_type}}})
Cost
1
Symbol
Affinities
Attack
50
Support
20
Range
1-2
Quote
"I'm alone. But I'm happy that way."
Skill 1
{{{skill1}}}
Skill 2
{{{skill2}}}
Support Skill
"Dark Mage’s Emblem" If your opponent has 5 or more cards in their hand, then your opponent must choose one card from their hand and discard it.