To enter the Euclid Coliseum, exit left on the ground floor of Euclid castle, and talk to the guy guarding the door.
In the coliseum, Cless/Cress (and ONLY Cless/Cress) fights eight monsters and a boss, by himself, to win prizes. He's only allowed to carry a small number of healing items during the fighting. After the eighth battle, Cless/Cress is healed up completely (unless the ninja intervene) to prepare him for the boss battle.
For the Coliseum, you'll want to equip the Eternal Sword, plus have a Gorgon Amulet and Body Amulet equipped.
For the first Lineups of the coliseum, use Teleport and Focus More for short range, and Soul Strike and Soul Forge for long range. I'll let you know what other skills to use for later Lineups.
If you fight all eight monsters but choose not to fight the boss, you only get 30,000 gold and miss out on prizes.
There are ten different prize packs you win from beating the coliseum. I'll list them below.
If you've gone to the Ninja Village, then the first time you beat all eight monsters, you'll fight Dozo and Okiyo after that (strategy below), instead of the boss. Regardless of whether you beat them or not, you don't get prizes after fighting them, but you do get to go to the Ninja Village (from Treant's Forest entrance, north three times, west three times, north three times) and if you talk to Lanzo you get a new skill.
Here's the rundown on the monsters you'll be fighting. Unless otherwise stated, you should just use regular attacks on each monster. Each Lineup is tougher than the last.
The worst monster you'll fight in the coliseum is Bigfoot. He can make himself spiky, so that if you touch him, especially if you're Teleporting and you land on top of him, you die. I don't know how I'd get through this if I was playing on a console!
Boss strategies are below all the Lineups.
-- First Lineup --
Round 1: Bugbear Round 2: Krakken Round 3: Mandrake Round 4: DarkVine Round 5: Draygen Round 6: Oak Root Round 7: Fe. Golem Round 8: Gorgon (use skills)
-- Second Lineup --
Round 1: Bugbear Round 2: EvilWeed (use skills) Round 3: Krakken Round 4: Fe. Golem Round 5: Gorgon (use skills) Round 6: Komodo Round 7: Mandrake Round 8: BearMan
-- Third Lineup --
Round 1: Udkala (back into corner and use Teleport) Round 2: DarkVine Round 3: Krakken Round 4: Gorgon (use skills) Round 5: Fe. Golem Round 6: Komodo Round 7: Mandrake Round 8: Bigfoot (use Teleport only and keep HP very high)
-- Fourth Lineup --
Round 1: Draygen Round 2: EvilWeed (use skills) Round 3: Krakken Round 4: BearMan Round 5: Fe. Golem Round 6: Komodo Round 7: Bugbear Round 8: FastStar
-- Fifth Lineup --
Round 1: Oak Root Round 2: BlueSoup (use skills) Round 3: Krakken Round 4: Gorgon (use skills) Round 5: Fe. Golem Round 6: Komodo Round 7: DarkVine Round 8: Solomond
-- Sixth Lineup --
TIP: You may want to equip the Rare Gauntlet for this lineup, as it makes Kemazotz's attacks less damaging. To make your life easier, use a Flare Bottle when fighting Kemazotz. Whenever Kemazotz's about to come above ground again, use a Flare Bottle right before so you can try to get in a powerful hit.
Round 1: Draygen Round 2: Udkala (back into corner and use Teleport) Round 3: Krakken Round 4: Gorgon (use skills) Round 5: Fe. Golem Round 6: Komodo Round 7: Oak Root Round 8: Kemazotz (hard and annoying fight, skills or no)
-- Seventh Lineup --
You may want to set Eir's Love as one of your skills for this lineup, as the Mimm battle can be tough, and she gives you a chance to use Eir's Love when she has her shield up.
Round 1: FastStar Round 2: BlueSoup (use skills) Round 3: Solomond Round 4: Bigfoot (use Teleport only and keep HP very high) Round 5: Komodo Round 6: BearMan Round 7: Gorgon (use skills) Round 8: Mimm (get close, but stay away when shield is up)
-- Eighth Lineup --
This Lineup is the hardest of them all. I recommend having Cless/Cress use Eir's Love as a secondary short-range skill, he'll need it in the Mimm battle. He can use it while she has her shield up.
Equip the Rare Gauntlets for this, to make Kemazotz less damaging, otherwise you will use all of your healing items during the first battle.
Round 1: Kemazotz (again, annoying and hard, skills or no) Round 2: Komodo Round 3: BearMan Round 4: Udkala (back into corner and use Teleport) Round 5: Fe. Golem Round 6: EvilWeed (try not to use skills this time) Round 7: Bigfoot (uh, yeah. Teleport only, HP very high) Round 8: Mimm (keep close but stay away when shield is up)
-- Ninth Lineup --
One of the previous lineups is picked at random, so if it's one of the tougher lineups, reset and start over from where you last saved.
-- Tenth Lineup and Beyond --
Like for the ninth, one of the previous lineups is picked at random. All you get for the prize are Gummies. It's not worth doing the eighth lineup over again just for a few Gummies >_<
-- Dozo and Okiyo --
Note that you don't get healed up after the eighth battle when Dozo and Okiyo intervene, so your HP and TP might be low. If your HP is below 6000 at the start of the fight, use an Apple Gummy first thing.
First use a Flare Bottle, then face left and use Teleport on Okiyo until she dies. If the Flare Bottle wears off, use another. When Okiyo is gone, use Teleport on Dozo until he's gone. If your HP goes below 6000, use an Apple Gummy at once.
When that's over, go to the Ninja Village as outlined above, to get a new skill.
-- Wyvern --
The boss you normally fight after the eight rounds is Wyvern, the same guy you fought in Moria.
Having the Golden Armor makes this fight a bit easier, because Wyvern's fire attacks will heal Cless/Cress.
Wyvern's attack is to fly at you and hit you with its claws. He can do a lot of these attacks in succession, hurting you pretty bad, so if your HP goes below 4000, use an Apple Gummy (or if you see that Wyvern is about to cast a spell, just let him cast it since it might be the Explode spell which heals Cless/Cress).
You'll want to use regular jumping attacks for this battle, since Wyvern is flying and is thus out of range of your skills. You *can* use Teleport if Wyvern stops to cast a spell or is floating above you, but do it at your own risk, because Wyvern is likely to hit you with its claws while you're stabbing and slicing with your sword.
-- Prize Packs --
1st win - Lion Teeth skill 2nd win - Souvenir Set - Soup Pot, S-Flag, Guinness 3rd win - Amulets Set - Body Amulet, Poison Amulet, Gorgon Amulet 4th win - Meats of the World - Veal, Boar Roast, Chicken, Steak, Sirloin Steak, Pork Roast, Dragon Steak, Beef 5th win - Herbs Kit - Verbena, Lavender, Sage, Savory, Red Verbena, Red Lavender, Red Sage, Red Savory 6th win - Bottle Set - Remedy Bottle, Rune Bottle, Medicine Bottle, Flare Bottle, Charm Bottle, Life Bottle 7th win - Magical Artifacts - Lipstick, Mage Ribbon, Magical Broom, Magical Pouch 8th win - Magician Star Set - Star Cap, Star Cloak, Star Broom, Star Rod 9th win - Fighter Star Set - Star Gloves, Star Helm, Star Shield 10th win - Gummy Set - Apple Gummy, Orange Gummy, Mixed Gummy, Miracle Gummy
After the 10th win, you'll always receive the Gummy Set if you win again.
The herbs from the 5th win are the best things you can win from the tournament.
You might want to aim for the prizes from the 7th win. It's the only way you can get the Lipstick, which can be useful, because it's like a random-percent-off Charm Bottle that you can use infinite times (the percent you get reduced changes each time its effect wears off). But you probably have plenty of money at this stage of the game anyway.
Also from the 7th win, the Magical Pouch sometimes makes random items appear in your list if you walk with it equipped. I've tried it before and nothing appeared in my list, so I didn't think it was that great. I have no idea what sorts of items it can make appear in your list, but I'm assuming probably the battle-use stuff.
You may want to go for the Fighter Star Set, because the Star Gloves are good for Chester, but the lineup before it is hell! And besides, you can get them in the final dungeon, and anyway you're probably not going to be using Chester much at all at this point.