If a player has any emblems or indefinite effects that need to be tracked (such as Start your engines!, the number of extra turns remaining, or max hand size modifications), they will be displayed in floating boxes on the far left side of their half of the battlefield and can be hovered over for additional information
While Carmen is undeniably powerful, she'd benefit more from a deck that's primarily focused on causing players to sacrifice cards and not necessarily a Vampire-themed token deck
I rank a free Repulse over a free Boomerang since card flow is so important at the kitchen table, but they are pretty close in my mind
But for common cards, anything diamond or below
Lastly, they come into play tapped, which is a significant enough cost to prevent you from running only surveil lands and tends to reward decks that develop at a more casual pace in my experience