The players have crossed the swollen stream and just found a piece of torn clothing belonging to one of the missing children.
Call for listen rolls DC:25 (2E INT -4). If no one makes it they notice the trail enters a large pool/puddle and disappears. Then call for another listen check but at DC:20 now (2E INT -2).
When someone makes it tell them that “The wind carries the sound of a child’s mournful cry.” With some effort they can listen for the direction and barely make out it comes from the northwest. When they head that way they come across the male child Daniel sitting in the mud next to a huge old tree crying hysterically, he is unable to even move due to the strong winds that buffet him . When he sees the PC’s light he calls out “mommy” hoping it is her.
As the party goes to help him out of the mud hole, something large drops out of the huge tree onto one of the party members, automatic surprise round. It is a Girallon HP 52 MM 104 3E. It will attempt to kill everyone since they are so close to its lair. It will not retreat but will become berserk if its hit points go below 50%. Berserk mean the beast gets +4 to STR and CON.
Note: The weather is so bad that missile weapons will be impossible and even spells have a 25% chance of failing due to difficulty of concentration. Anyone covered in mud from any earlier falls or knocked down in this fight must make a DEX roll (DC 10) to get back up.
Once the Girallon is dead Daniel can be questioned by the party. He is barely coherent, he states that a different one took his sister, a bigger one. If asked Daniel will state that the creature that attacked him was a Bogeyman. It dropped him here a few minutes ago and he has been trying to get out of the mud since then.
The characters are now in a quandary, they cannot go back to the village with only Daniel, and sending one person back with Daniel may be impossible due to the river and poor visibility. They will have to bring him along and of course protect him, hindering them even further. Daniel points northward to show the direction the creature took his sister. Sure enough a set of footprints continues on that way. After a hundred yards or so the players can see the entrance to a cave, half submerged by the rising flood waters.