A: The box comfortably holds 100+ standard MTG cards with sleeves
You know those Dragon's Rage Channeler Izzet decks
Masterpiece Series MTG: Exceptionally rare, alternate-art foil versions of powerful cards, like the Kaladesh Inventions or Amonkhet Invocations
If the numbers mean nothing to you, let me jog your memory
The additional line of text on Murktide Regent just makes them unnecessarily big sometimes, as additional instants and sorceries that get exiled, give him more and more +1/+1 counters
For example, Captain Storm, Cosmium Raider from the Lost Caverns of Ixalan release has an ability that says "Whenever an artifact enters the battlefield under your control, put a +1/+1 counter on target Pirate you control." If an artifact creature enters the battlefield under your control, that ability won't trigger