Easy level up side quest-by Jeremy:

When you are asked by Viktor to go to obtain Tsai for the battle instead travel northward to Toto. When you get there travel directly forward till you see a left turn, take it and you should be on a bridge that connects to Muse. Follow the path until you reach Muse on the world map then follow the northward path leading from it. Follow this path until you come across a fork in the road take the left path and follow it till you reach the Muse/Mathilda checkpoint go forward until you come to a wall, push on the wall until you can move out from behind it then go forward till you are out of the checkpoint. On the world map there should be a path follow it and run from any battles [be sure to save in Muse just in case]sooner or later you will come to a town called Highway Village. Go directly to the inn and save, when you're done that search for a man named Humphrey, he will offer to pay your lodgings for a night when you wake up go outside and you should see a boy named Futch talking to his friend. Talk to Humphrey again and once again he will offer to pay for your lodgings.when awake go outside toward where you saw Futch talking to his friend, there should be a man talking to the boy Futch knows telling him there's a dragon on Mount Rakutai after hearing this the boy will run off go back to the inn and rest free thanks to Humphrey. Wake up and go downstairs there should be a big commotion about the boy missing tell Humphrey you will help him and go out into the world map and train until level 35-40 then go northward till you enter Rakutai Mountain battle the harpy and win [I advise you to equip the hero with fire and Jowy with lightning you can also equip water to Nanami if you were able to afford it in Muse] when you're done that request for Humphrey to join you he will after that you can either choose to train more or simply return to the Mercanary Base.
Sent in by: vileserpentking

Best Ending  -  To get the best ending, you must have all 108 characters before you talk to Shu about the Rockaxe mission. Also when you near the end of Rockaxe Castle, when Nanami jumps out to protect you from Gorudo, you must answer very quickly (doesn't matter which answer you choose). If you did this correctly, after Dr. Huan reports of her unfortunate condition, he should ask to talk to Shu in private.

Did all that? Alright, then once you've beaten the game, head back to Tenzan Path (northwest of Kyaro) and return to that place by the waterfall. Jowy's there, of course, and you'll go into a duel with him. Just keep on defending throughout it. After that, he'll ask you to take his Black Sword Rune. Keep on refusing. Once you've refused enough, Leknaat will appear. I won't spoil the rest, but those are the requirements for getting the best ending. 

Early Level Up Trick  -  When you are spying on the Highland camp, at the end you get attacked by Highland soldiers. After you beat them, Jowy will hold them off while you run to Nanami. When you reach her, you fight more Highlands (use Bright Shield to defeat them easily). After that she asks where Jowy is. Reply ".....", and more Highlands appear. After the battle she asks you again. Keep replying "...." to fight more Highlands every time. Keep using Bright Sheild until it runs out, then use Flaming Arrows from the fire rune. After the runes run out, use Family Attack on the one with the spear and just attack the rest, (if you're not around level 20 this can be difficult) Anyway, the first couple battles should give close to 1000 experience each. Keep doing that until your levels are pretty high (or they stop giving you less than 100 experience). 

Random Name  -  When you are supposed to enter a name, press L1 + R1 or L2 + R2 to choose a name at random. 

Random Teleportation Trick  -  When you get Viki in your group and ask her to teleport you somewhere, once in a while she will teleport you in the wrong place. One of which is a hidden room in Radat town. Here you'll find many nice items. 

Recruit Tetsu  -  To recruit Tetsu get Alex (the item keeper) in your group and when he sells fried tacos buy 3. Next go to Lakewest and keep giving them to your hero. Once you done that steam should start coming out of your hero. Then go and talk to Tetsu and he will ask if you like baths and answer I love baths then he will say something and will build a sauna for you. The sauna is where you enter in the front not by the bar. 

Recruiting Clive Tip  -  When trying to recruit the 108 stars, make sure in Muse you talk to Clive. If you do not do this he will not appear in South Window and you can never get him.

How to beat Luca Blight Easily - Whenever you are asked who to put in the groups of attackers that will be facing Luca, leave all of them blank except for Hero. You will eventually come to the battle against just you and Luca. For some reason he wont be able to attack back when its just against you. Since he has a load of HP, it will take a long time but eventually he will die without giving you a scratch! The only downside to this is that now, your hero is levelled up really high and all your other characters are still low.

Color Intro - When you are preparing to jump into the river in the beginning, Rowd will have a group of soldiers attack you. When he runs off answer Jowy so that you won't jump off, Rowd will return with more soldiers. Do this 108 times for a color intro and to level up your characters as well.

Extra Boots - Before jumping off the cliff at the start of the game unequip the boots on Riou and equip them on Jowy. When Pohl asks you to get two pairs of boots take three from Barbara. Equip two pairs of boots on Riou and talk to Barbara again, she will allow you to take three more pairs of boots resulting in four free pairs.

Extra Flowing and Mother Earth Runes - Speak with the Rune Master at Gregminster and buy all runes that appear in Rare Finds. If there are no rare finds, then just select 'Quit'. Observe the cabinet behind the Rune Master and then speak with him again. There is a 60 to 70 percent chance that the Rare Finds will open up. Try this once during every trip to Gregminster.

Generate a Random Name for Hero - When you start a new game and it gets to the screen to name the character, make sure the name box is empty and highlight "Determine," press "X" and it will automatically generate a random name.

Hidden Room in Radat - When Viki teleports the hero from the headquarters to anywhere in the game, she sometimes mistakenly teleports you and says, "huh?". If you're lucky, you get teleported to the secret room in Radat, where there are some neat items.

Hidden Scenes - Bring Valeria to Banner Village to recruit Anita.

Bring Killey to Gregminster to recruit Lorelai.
Defeat Rowd in Kyaro when he comes to arrest you.
Speak to Gengen before you speak to Leona after you are asked to buy some flour from Ryube.
Take Flik or Viktor to Lakewest when recruiting Hix and Tengaar.
When running from the Unicorn Brigade, go north instead of east and examine just to the right of where you'll later leave the X mark. This is also a time saver.
Talk to Shu first the night before your battle with Luca Blight. Your responses trigger an extra scene with Apple the next morning.
Talk to Leona the night before you fight Luca.
Talk to Leona the night before retaking Greenhill.
Take different "pure women" with you to recruit Sigfried. We recommend Sierra or Mikumiku.

Instant Level 99 - When a character is at Lv. 39 (Lv. 49 with a Fortune rune), go to L'Renouille. Fight a group of Highland x6. Kill off all party members but him, then defeat the enemy. His level should shoot up to 99.

New save icon - First, acquire the five squirrels by walking along the routes surrounding Greenhill alone, or with other squirrels. After obtaining all five (which can be time consuming), check your memory card icon on your playstation. There should be a new icon, and you also get another scene at the end of the game for acquiring all five squirrels.

Play as McDohl - First, you must have save data from Suikoden loaded into the Suikoden 2 file. Then, after you beat Luca Blight, go to Banner Village. Talk to the hero lookalike, and he will tell you McDohl is here. Go east of the inn to see Gremio or Ellie blocking the way. Go talk to the lookalike again, and he will divert attention. Talk to McDohl, and Gremio/Ellie will eventually tell you Ko, the lookalike, is gone. You, McDohl, and Gremio/Ellie go off to find Ko in the path to Gregminster. At the end, you will be face to face with Lepant, who offers McDohl the presidency. He and Gremio eventually go to their house in Gregminster, where he can be recruited at any future time.