When a card that selects a card in the Graveyard as a target, such as “Monster Reborn”, “Mask of Darkness”, “Magician of Faith”, “Spear Cretin”, or “The Shallow Grave”, is activated, you may chain “Disappear” to remove the targeted card from play, and the “Monster Reborn”, etc., will resolve without effect. This is because these cards select their target at activation, not resolution.
“Bazoo the Soul Eater” removes a monster in the Graveyard as a cost, so you cannot chain “Disappear” to the effect of “Bazoo the Soul Eater” to negate it. The monster is already removed from play before you can activate “Disappear”.
If you chain “Disappear” to your opponent’s “Backup Soldier” you can remove one of the targeted monsters from play, but the remaining two (or less) go to the opponent’s hand.
Netrep Rulings:
“Disappear” may not be activated in the Damage Step.
“Disappear” may be activated in a chain with an effect that removes a card from the Graveyard.
“Disappear” may not be chained to the effect of Special Summon monsters that are Special Summoned through removing monsters from the Graveyard in an attempt to prevent the Summon.