The First Sliver is a great choice, but getting more eyeless pretties onto the battlefield isn't helpful if they all die in a Fumigate
It doesnt get around that one-land-per-turn restriction, but theres plenty of other ways to do that
When it enters the battlefield, it blats each player in the face, dealing one point of damage for each non-basic land they control
Effects that say the enchanted creature can't be regenerated won't prevent umbra armor's effect from being applied
There are also a handful of one-off mechanics and keywords that appear on Silverquills students, staff, and spells
According to what I wrote, at the moment Counterspell is being played only in blue-red Murktide, among the tier ones of the format