Goblin of Greed

Edison Card Text
As long as this card remains face-up on your side of the field, neither player can discard from his/her hand as a cost.
Dark Crisis • 2007-12-12
No targeting
No Damage Step effect
Banlist • Unlimited
Rulings
edisonformat.net
●Goblin of Greed prevents discarding as a cost, but not as part of an effect. So Goblin of Greed will stop Kuriboh, but not Mirage of Nightmare or Graceful Charity.
●If your opponent activates an effect and discards as a cost, and you chain Call of the Haunted to Special Summon Goblin of Greed, he doesn't stop the effect because the cost was already paid.
edisonformat.com
"Goblin of Greed" prevents discarding as a cost, but not as part of an effect. So "Goblin of Greed" will stop "Kuriboh", but not "Mirage of Nightmare" or "Graceful Charity".
If your opponent activates an effect and discards as a cost, and you chain "Call of the Haunted" to Special Summon "Goblin of Greed", he doesn't stop the effect because the cost was already paid.