The inability to make mana for things like Nissas Pilgrimage, From Beyond, Nissas Renewal, Ugin, the Spirit Dragon and basically any plain ol spell restricts you to a very creature-heavy build
There are also several cards that would be better in a different deck, which means they are easy cuts, but it takes time to learn which cards these are
I have a foil Coveted Peacock Ive been wanting to find a home for and I think Im going to give it a try here
Any deck that makes proper use of these counters enjoys the monarch because they have a ton of creatures to defend or secure the monarchy
Amusingly, your opponents will probably need a non-creature spell to take it out, so you might get one last draw on the Sentinel's way out
Keep your eyes on the official Secret Lair site