Some of the cards from The Horde expansion have been modified to accommodate the co-op version.
Their effects are replaced with the following.

By playing this spell, you can put a monster to sleep (not the final monster). That monster will not attack during its next turn.

By playing this spell, you can poison any monster in play. Place 1 Poison token on its card. You can also target the final monster. The poisoned monster loses 1 Life point before attacking for each counter on it.

With this spell you can revive one of the monsters (not the final monster) that you have already defeated during this adventure. The monster gains the Defensive ability and has 5 Health points.
Mind Control can't be used on Bahamut.

Only in this new co-op mode, this knife allows you to reduce to 0 the armour value of the attacked Monster.
The Weapon with this effect when played against a Monster has a different secondary effect.
For each card which would have been discarded by an opponent in the classic PvP game the armour
value of the defending Monster is reduced by one.
This secondary effect is ignored if the defending Monster has no armour bonus.
Only in this new co-op mode, this ability allows you to replace any loot cards in play with a new one of the same type.
Draw a new card from the same deck and place it in the same area of the removed card.
Put the removed card on the bottom of it’s deck.