After you follow Geno through the forest, you find Bowyer, who is responsible for raining arrows on the people of Rose Town.
Geno with join you in this fight. He has the Special ability Geno Beam. If you hold the Y button, then let go when there are three stars on the screen, you will increase the power of the attack.
To get bonus damage with Geno's regular attack, you have to press the button when you can still see Geno's eye, just before he turns to face the enemy.
Bowyer doesn't have any elemental weaknesses, so just use your strongest attacks.
After one turn, Bowyer will make three buttons appear in the area. Eventually, he will shoot an arrow at one of these buttons, locking it. You will not be able to use the button that Bowyer has locked, so you will either not be able to use Special attacks, or items, or regular attacks.
Bowyer can attack with Bolt, a lightning attack on one character. This is unblockable.
Bowyer can also shoot an arrow at a character. You can block this by pressing the button when the arrow is to the left of Bowyer's face.
Bowyer can attack with Static E, an electrical attack that hits all characters.
He can attack with G'night, which inflicts Sleep on one character.
After the battle, there will be a cutscene. Be sure to use the Flower Box that you won from the battle. You can't go down the tree stumps in the area where you fought the boss, so just go northwest to exit the forest. From there, you should first go back to Rose Town.
Go into the Inn in Rose Town and talk to Gaz. After a cutscene, you will get the Finger Shot, a weapon for Geno. Be sure to equip it.
Use the southwest exit to leave Rose Town, then go west. You can optionally go into the Pipe Vault.
After you're done in the Pipe Vault, go west to Moleville.