Grab the Reins [Mirrodin] DP12 Monsters lose 500 ATK for

Monsters lose 500 ATK for each Venom Counter on them

If you Normal Summon it this way

Set: Stronghold Type: Creature — Sliver Rarity: Uncommon Cost: {W}{U} All Slivers have shroud

you can send up to 3 cards you control to the Graveyard to look at your opponent's Extra Deck and send the same number of cards you sent to the Graveyard

Grab the Reins [Mirrodin] DP12 Monsters lose 500 ATK forSet: Mirrodin Type: Instant Rarity: Uncommon Cost: {3}{R} Choose one Until end of turn, you gain control of target creature and it gains haste. Sacrifice a creature. Grab the Reins deals damage equal to that creature's power to any target. Entwine {2}{R} (Choose both if you pay the entwine cost.)