I don't know what would be a good effect, but its description has to be a haiku.
Example:
When you play a pair,
Gain mult equal to the rank
of the top card played.
#Haiku Joker
hybrid shadow
||yada yada this isn't a haiku, "top card" isn't proper terminology yada yada||
heavy geyser
I got a laugh out of this so it has my support
smoky sedge
When you play two 5s and a 7 in the same hand, get $6.
When you play two fives
and a se-ven in the same
hand, get 6 dol-lars.
(The break between same and hand is a little weird, but it counts!)
Thing is, you've now opened up a can of worms that is other rhyming schemes, like limericks.
glad yacht
When a Flush is played,
Get the whole sell value paid,
Tarot Cards the name.
When a flush is played, Get the whole sell value of your current held tarot cards.
ocean ledge
In Japan they do not care too much about the 5-7-5 rule, as long as it sounds and flows well. The hard fixation on this rule is a western world invention.