Rancor
Color=Green
Type=Enchant Creature
Cost=G UL(C1)
Text(UL+errata): Enchanted creature gains +2/+0 and has trample. ; When ~this~ is put into a graveyard from play, return ~this~ to its owner's hand. [Oracle 99/05/01]
Weatherseed Treefolk
Color=Green
Type=Creature - Treefolk
Cost=2GGG UL(R1)
Text(UL+errata): 5/3, Trample ; When ~this~ is put into a graveyard from play, return ~this~ to its owner's hand. [Oracle 99/05/01]
Serra Avatar
Color=White
Type=Creature - Avatar
Cost=4WWW US(R1)
Text(US+errata): */*. ~this~'s power and toughness are each equal to your life total. ; If ~this~ would be put into a graveyard from anywhere, shuffle ~this~ into its owner's library instead. [Oracle 99/05/01]
Its power and toughness are continuously calculated. [Urza's FAQ 98/10/05]
It shuffles itself into the owner's library no matter where it would go to the graveyard from. Discard, destroy, counter, Millstone, etc. [WotC Rules Team 98/10/18]
If it goes to the graveyard from play while its abilities are nullified by an effect such as Humility it actually goes to the graveyard. [WotC Rules Team 98/10/18]
The ability to shuffle into the owner's library is a replacement effect (see Rule T.10). It applies even when this card is being put in the graveyard as part of a cost or a mana ability effect. [D'Angelo 99/05/01]
The ability replaces the "put into the graveyard" effect, so nothing which triggers on it going to the graveyard will trigger. But, since it does not replace the entire action that put it into the graveyard, anything which triggers on that action would still trigger. For example, a "destroy", "discard", or "counter". [Barclay 99/03/30]
Planar Void
Color=Black
Type=Enchantment
Cost=B US(U1)
Text(US): Whenever a card is put into a graveyard, remove that card from the game.
The card does go to the graveyard before it is removed from the game, so other triggered abilities like Energy Field will trigger on the card going to the graveyard. [D'Angelo 99/01/12]
It will trigger on itself going to the graveyard from play and remove itself from the game. [D'Angelo 99/01/12]
It will trigger on any cards going to the graveyard at the same time it does, and it will remove them from the game. [D'Angelo 99/03/06]
If Disenchant is used on it, Planar Void goes to the graveyard (and removes itself), then Disenchant goes to the graveyard and stays there. [DeLaney 99/01/18]