What “secret tech” cards make you feel like a genius for running in your deck?

These are cards that most people have either never heard of or never seen used properly before.

For me, it would be [Undercity Informer] used in my [Jarad Golgari Lich Lord] deck. It is a 1 generic mana sacrifice outlet, that will mill target player until they hit a land. I can use it to mill myself and fill my graveyard up, or ruthlessly mill someone out with enough mana/creatures. I think it is such an underrated gem of a card and sacrifice outlet that should see more play in self mill decks or just aristocrat decks in general.

What are some of your “secret tech” cards??