Ooh ooh I know I know:

[[Dead Reckoning]]

Play it on turn one. It goes directly to the graveyard. Then when you need some good removal, play dead reckoning to bring it back, pinging an enemy's creature for 13 and effectively removing it. Bonus -- you get Death's Shadow back, just when you need it. It's a tutor+removal for 4 mana!

[[Cragganwick Cremator]]

Though it's not a combo using Death's Shadow from the graveyard, how about pairing it with Hatred. You get effectively double the bonus from each life paid.

[[Hatred]]

Since they're valid in standard:

[[Platinum Angel]]

107.1b Most of the time, the Magic game uses only positive numbers and zero. You can’t choose a negative number, deal negative damage, gain negative life, and so on. However, it’s possible for a game value, such as a creature’s power, to be less than zero. If a calculation or comparison that would determine the result of an effect needs to use a negative value, it does so. If such a calculation yields a negative number, zero is used instead, unless that effect sets a player’s life total to a specific value, sets a creature’s power or toughness to a specific value, or otherwise modifies a creature’s power or toughness.

Cards that cause you to lose life (some examples from here), although most or all are not standard legal:

[[Doomsday]] [[Ambition's Cost]] [[Infernal Contract]] [[Maralen of the Mornsong]] [[Night's Whisper]] [[Pain's Reward]] [[Phyrexian Arena]] [[Pox]] [[Reanimate]]

[[Pain's Reward]]

I'm kind of curious with this one, if you were to have Platinum Angel in conjunction with Death's Shadow, would you go even more negative? Such as if you bid 100 life, would you be around -100 life? If so that's pretty devastating consider Death's Shadow can be a 100000000000000000000000000/ 10000000000000000000000000000.