Showing a card with a Joker on it is not buidling up a character.
Yes, I know how the card was meant, Ive read Year One, too, but building up a character is for me when he actually does something and not throws a card away offscreen.
See to each his own.
I prefer a tease like that, Thanos we've seen... what 3 times now, and it loses it's appeal each time we don't get the pay-off.
We got the Joker tease... and then we got The Joker.
Set-up and delivery.
I consider that a solid build.