Well, take the Penumbra ability in Apocalypse (When x is put into a graveyard from play, put a equivalent black creature in play).

Now, take Lifeline, a Rare in Urza's Saga:

5, artifact

Whenever a creature is put into a graveyard and another creature is in play, return the first creature from that graveyard to play under its owner's control at the end of turn.

So, whenever your penumbra creature dies, you'll get it back at the end of the turn, since its shadow version will still be in play, assuming it hasn't been killed somehow.

However, you have to make sure your OPPONENT doesn't get the benefits of lifeline, get some cards that remove creature cards from opponent graveyards. Phyrexian Furnace, Night Soil, and Eater of the Dead are good choices. If you can't get any of these out, just hope you outnumber your opponent in creatures. If you want, you can use Mortuary instead of Lifeline, but that'll seriously slow down your library (trust me).

Hope somebody uses this.