Gifts Ungiven: Its an easy combo-enabler, mostly because its an instant
The set will introduce a slew of new mechanics, including Outlaws (defined as creatures with the Assassin, Mercenary, Pirate, Rogue or Warlock subtype), Crimes (which are committed when a player targets an opponent or any of their spells, permanents, or graveyard), Spree (an addition to modal type spells), and Mounts and Saddle
Treacherous Terrain The effect is definitely a little slow, but Treacherous Terrain can be the card to finish the job in a long and grindy game of Commander
I prefer her as part of the 99 of a Dragon Tribal deck, but she's also fine as a commander, especially if you build a Token / Sacrifice subtheme with her and cards like Parallel Lives
Example: A player casts Cytoshape, causing a Kruin Outlaw (the front face of a double-faced card) to become a copy of Elite Vanguard (a 2/1 Human Soldier creature) until the end of turn
While the first two battlegrounds are great for starting out, two more are included to give players even greater challenges with Deep Trouble