How to get here: Talk to Twilly and choose "Moglin Forest"

Twilly: Wow! You must be brave! The Moglin Forest is a dangerous place to test your skills. Fight until you drop!
Choose "Great! let's start!" or "Maybe next time"

Choosing "Maybe next time" takes you back to Battleon.

Choosing "Great! let's start!" :
Twilly: To make this a fair challenge, I will hold onto your potions till the battles are over. I will heal you up after a few battles.

Then you fight a monster from the list below.

You start off Fighting:
Deathwood
Drakel Warrior
Frogzard
Giant Spider
Snayl

After 5 Wins:
Drakel Power Scout
Gnarl
Mantik
Mawler
Mud Golem
Undead Soldier
Undead Troll
Wild Worm

After 10 Wins:
Chrask
Toadzard
Velociraider
Whomp
Worm Caster
Worm Knight
Young Minotaur

After 15 Wins:
Cyclops
Demon Tree
Elite Frogzard
Forest Demon
Gorarog
Grizzle
Kresh
Lesser Warbeast
Red Moglinster
Ruby Golem
Troll

After each win:
Twilly: Nice job! You really are strong. I bet you will beat lots of monsters! Ready for another?
Choose "More! More! More!" or "I am done for now"

Choosing "More! More! More!" puts you in another battle.

Choosing "I am done for now" takes you to Battleon.

Each win gets added to the Moglin Forest Wins total on the top of the screen.

Every 5 wins:
Twilly: You must be really tired after all that fighting. Need any healing?
Choose "Yes!" or "No thanks"

Twilly: I am a little low on power right now, but I will heal you up as much as I can.

When you leave:
Twilly: Here are your potions back. See you later!

Source

Suikoman444, http://forums2.battleon.com/f/tm.asp?m=2929253