Alrighty, here's how it works:
Card of safe return will allow you to draw a card from your deck whenever a monster is special summoned to the field from your graveyard.
Manticore of Darkness has a "tag team" revival effect. During the end phase that Manticore is sent to the graveyard, you can discard one Beast, Beast-Warrior, or Winged Beast type monster from your hand or the field to the graveyard to revive it.
So when done right, the following can happen. Let's say Card of Safe Return is active. Activate Tribute to the Doomed, tributing a Manticore of Darkness and destroy one monster on your opponent's side of the field.
Now we hit your end phase. Manticore's effect activates, Let's say you have another Manticore in your hand, go ahead and discard that to revive the current Manticore in the graveyard. Now Card of Safe Return activates and you draw a card.
Well, you now have another Manticore in the grayeyard and it is the End Step. Go ahead and discard another card (hopefully another Beast-Warrior you just drew, maybe even your third Manticore, to revive another Maticore, draw a card.
If all works out perfectly, you now have 3 Manticore's on the field without really paying much to get them there. Now if they get destroyed or such during your next turn, you can use this draw/revival technique again. You could possibly use Manticore as a tribute for a tribute monster and get its effect too.
Now since you can also use monsters on the field for Manticore's tribute requirement, you could also have two Manticores continuously reviving each other, while drawing a card at the same time. This plays in nicely for an Exodia deck for a fast draw to win.
Hopefully this make sense. I haven't done the combo myself, but was reading up on the hype when it was discovered.