Lessons / Before Your First Night
How to trade a real tile for an exposed joker.
You can make a joker exchange without freezing.
A free American Mahjong lesson from June. About 3 minutes.
Next lesson: What to do when you're lost
Green Dragon pung with a joker
Their pung, your Green
The joker is yours
Green swapped in, joker taken
Short version: if someone has an exposed group with a joker standing in for a real tile, and you have that real tile, you can trade it for their joker on your turn. Watch for it every turn.