Do you have a pet card...

[Cosmic_Insight]

Fogs are sooooo underrated, and one of the best new ones is Obscuring Haze. Most of that cycle is expensive and unliked, but stealing a game or finding a way to stay alive with a fog is always fun - and people in EDH like that kind of stuff.

https://deckstats.net/decks/154264/1930298--/en

This deck of mine loves fogs, and should probably use a few more. Kind of inspired to write some sort of primer on fogs, would anyone be interested?

[Bonethousand]

Brash Taunter all the way, babyyyyyyyyyy.

[PaladinKnightLord]

If I had to choose just 1 card, Beloved Princess. Not only is it cheap, but if you pump its power and toughness enough, it can't be blocked by anything it can't kill.

A lovely combo with Entangler and Darksteel Plate makes her a wonderful defender. Stop all attacking monsters, gain life thanks to lifelink, and she can't be destroyed.

[Grimjack]

Perplexing Chimera.  I love the interaction &frustrations this card brings in my Cube and for EDH

[anjinsan]

I could write a whole article on Knowledge Pool.

I'm not sure it quite gives me "joy to play"; I kinda tend to have to sit and explain it to people, and whilst some people love it others hate it. It's cool if it comes up occasionally, but I don't want to see it every game. But I DO want to see it - it's just such an interesting effect and has a lot of less obvious and slightly-surprising synergies (beyond just the "you can't case spells" combos, of course), and can cause some weird and unpredictable board states that require a bit of thinking.