The interaction between modular creatures and -1/-1 counters is incorrect:
Gatherer rulings for
Arcbound Ravager:
If this creature gets enough -1/-1 counters put on it to cause its toughness to be 0 or less (or the damage marked on it to be lethal), modular will put a number of +1/+1 counters on the target artifact creature equal to the number of +1/+1 counters on this creature before it left the battlefield.
Similar problem might exist with
Kinsbaile Borderguard.
Elite Arcanist doesn't lose its card when it leaves the battlefield.
Frenzied Goblin targeted ERROR even when there are legal targets on the battlefield (
Frenzied Goblin itself is also a legal target, of course).
When
Unexpected Results finds a land, you should get a choice whether to put it on the battlefield and return
Unexpected Results to your hand -- it's not automatic.
I attacked with AEtherling and after combat damage exiled it -- it returned tapped.
I blocked 1/2
Tarmogoyf with
Snapcaster Mage. No creatures in either graveyard. Result was that
Snapcaster Mage died and
Tarmogoyf got the creature boost and survived. Both creatures had lethal damage so both should die.
In a complex scenario involving
Infinite Reflection on
Master Biomancer, it seems that when new creatures enter the battlefield, they only get 2 counters per Biomancer, ignoring +1/+1 counters on THEM.
Cavern of Souls should be automatically tapped for colored mana when possible, even when there's only colorless mana requirement.
Ravager of the Fells gives you "
Cancel" option when targeting a creature, which cancels the whole ability -- targeting opponent and dealing damage to him should be mandatory, though.
When clashing, I'm not told whether opponent kept the card on top of library or put it on bottom. Similarly, scry should give you similar messages.