If you have your opponent’s “Pot of Greed” in your hand because of “Exchange” or “Graverobber”, you CAN send your opponent’s “Pot of Greed” to the Graveyard to activate your “Avatar of the Pot”’s effect. But if you did this with “Graverobber”, you take 2000 points of damage to do so
“Barrel Behind the Door” cannot be activated against cards that do not inflict damage when the card resolves, such as “Graverobber”, which inflicts damage later.
“Des Wombat” will protect you against the effect damage of “Graverobber”.
Netrep Rulings:
If “Graverobber” is chained to the effect of a card that would remove a Spell Card from the game by any means than as a cost, “Graverobber” may target that Spell Card to remove it from the Graveyard before that effect resolves.
A continuous Spell card retrieved by the effect of “Graverobber” and then played remains on the controlling player’s field as normal until that Spell Card is removed from the field.