The Wood Toad is quite elusive, having only a 20% chance of spawning and being initially under the Invisible status. It is recommended to enter the area after chaining at least ten Malboro Kings to increase the odds of it appearing.
The Wood Toad is located in the upper portion of the Corridor of Ages area of the Salikawood near the dead end with the Malboro King, although the player might not see it since it is invisible. If the player hears a sloshing sound or sees a distortion in the air, casting Reflect on a party member and then bouncing a spell off them will reveal the enemy.
An alternative is to have the Wood Toad uncover itself by means of luring another enemy to its spot. Usually, a Baknamy or Malboro King will be around the stairs, and if the player lures either near the Wood Toad and attacks them, it will go out of stealth mode.