There are three cards that create subgames in Un-sets and Enter the Dungeon is a fun one to play
It's very powerful once this becomes Ajani, Nacatl Avenger, especially in a cat deck
If you have a limit to spend around $100 on a deck, this will help you narrow your choices and keep your budget in mind
That means you can still throw them into a blender for other sacrifice outlets, like Blood Artist or Phyrexian Altar if you need to
The Mirror Play or Draw: -2 Venerated Loxodon, -2 Emmara, Soul of the Accord, -1 Saproling Migration, -1 Legions Landing, -1 Shanna, Sisays Legacy, -1 Shalai, Voice of Plenty
Copperhorn Scout: good if your opponent is tapping your creatures before combat