Bringing them Back (and sometimes keep it!): Adarkar Valkyrie Sac an opponents creature, then get it permanently
Best case scenario, you remove two small creatures and draw a card
Often too difficult to cast, the upside is rarely worth destroying your mana base for
Be aware that some players will fear Vito, Thorn of the Dusk Rose because of those Sanguine Bond combos and try to kill you on sight
This keeps Polymorph fodder up, all while having creatures in the air that can attack for damage if need be.
That's very Golgari, but now you trade green for blue, and in doing so you open yourself up to mass card draw, filtering, counters, bounce, stealing, copying, and many more effects