Most notably, if a triggered ability asks its controller to pay a cost, you pay that cost for the copy if you wish to have it paid
1 Leonardo's Technique Sorcery Taking the top spot for us is Leonardo's Technique, which allows you to return two creatures from your graveyard to the battlefield, provided they cost three mana or less
Estinien has loads of interesting things going on, from getting aggressive with a leader you can send in the air to incentivizing both non-creature spells and dragons
Next on the list might be casual players who actually want to build decks around the cards, but I'm not sure how often this happens
The only thing stopping the Thraben from completely charming me is that Get Lost exists and is pretty much strictly better
I like the last ability, but if you slap this in the command zone, its for the mana