At this point most players will start wondering, "What do they have to stop what I'm planning?" Abeyance takes away all that worry, while greatly increasing the chance of victory during an attack (or defense) by preventing the opponent from playing "instants, interrupts, sorceries, or abilities requiring an activation cost"
Squall is your primary attacker, while the creatures either control the battlefield or give Squall extra stat boosts
Also really screws people over who want to tutor to the top
Additionally, whenever Umbris or another nightmare or horror enters the battlefield under its owner's control, target opponent exiles cards from the top of their library until they exile a land
The ratios are quite good and fitting for a Control deck: lots of slow grindy value and a variety of interaction to slow down opponents long enough to let you grind them out