Flip a coin. If tails, this attack does nothing. Either way, you can't use this attack again as long as Farfetch'd stays in play (even putting Farfetch'd on the Bench won't let you use it again).
A mail-in prize draw offering another copy of the Japanese CoroCoro print was published in the December 1998 issue of CoroCoro Comic, released on November 15, 1998. People wishing to enter the prize draw were required to affix the application ticket on the bottom left of the article page to a postcard and send it to Shogakukan. Two thousand winners were sent a set of five cards mounted on two plain sheets: Surfing Pikachu and Flying Pikachu on one; Jynx, Cubone, and Farfetch'd on the other. Both the CoroCoro insert and the three-card sheet contain accessories to be used with the attack effects of Jynx, Cubone, and Farfetch'd: a Curse marker, a Bone counter, and a Leek counter, respectively. The Base Set print was reprinted in Base Set 2.
The Japanese Unnumbered Promotional print slightly rewords the effect of the Leek Slap attack to put the "you can't use this attack again" clause before the coin flip. While the Leek counter included with this print is not specifically required, it can be used as a visual aid to show if the attack has been used. GX markers would similarly be introduced during the Sun & Moon Series for the single-use GX attacks.