The level 99 trick involves dying after this level increase, and then repeating the process over and over until you get to level 99. This is rather tedious, but there are methods to make sure things go smoothly.
The flow of this entire process is--
1) Save file at Brass Castle cots.
2) Talk to Louis to start event.
3) skip through dialogue intil major battle starts.
4) defeat all enemies and proceed to Amur Plains.
5) remove all armor, and get killed by enemies.
6) select "don't give up" after getting killed, and start over from 1.
Here are steps you can take to make this easier.
1) Do not train anyone's skill in "repel" or "parry" if you don't need to.
This is because if your repel and parry skill is too high, it would be difficult for you to kill yourself after you receive the 2 level increase. Dying fast becomes a problem after you reach higher levels, and you need to make sure you can die fast to reduce the amount of time spent.
2) Do train the "Armor Protect" skill for Chris, Borus, and Roland.
Although wearing armor would make yourself harder to kill, you can also remove armor, making it easier for you to get killed after the major battles. However, it is also important to survive the major battle, so increasing your armor protect skill would help. Also, making sure you have the best armor possible would help. Go to Vinay del Zexay's Merchant Guild hall to buy the best stuff you can purchase (Chris has a lot of money), especially the accessories like Winged Boots and Power Gloves.
3) Gain levels at Amur plains before trying this trick.
Before you go to the Amur plains, you can't really get your levels above 21. However, at the Amur plains, you can easily get yourlevels up to 30, and if you persevere enough and defeat the Troll Dragon (area boss), you can get your level up to 34 easily. This not only halps with the survival rate during major combat but also gets you extra skill points as well as cuts down on time.
4) Use the Chris/Borus unit as the only combat unit in major battle.
There are four units in major combat--
1. Chris, Borus, Zexen Knight, + Salome as Support
2. Roland, Zexen Knight x 3
3. Zexen Knight x 3
4. Zexen Infantry x3
In contrast, the enemies are--
1. Dupa, Karaya Warrior x3
2. Shiba, Karaya Warror x 3
3. Bazba, Karaya Warrior x 3
4. Lizard Warrior x4
5. Lizard Warrior x4
6. Lizard Warrior x4
7. Lizard Warrior x4
8. Lucia, Karaya Warrior x3
9. Beechum, Karaya Warrior x3
10. Karaya Warrior x4
So, as you can see, you are against some stiff competition.
When your level is still under 50, the only unit that can have any power is Chris's unit. Chris herself is a killing machine. Even if Borus ends up getting killed, Chris is nearly impossible to defeat. So make sure she is in the center of the battle field so all enemies can attack her instead the other weaker units. Even if Chris is surrounded on all four sides, she can take them all down herself. As long as her attack skills are maxed out, along with her armor skill (but don't raise her repel, and ease up on parry), she turns into the goddess of war.
After you reach above level 50 or so, the major battles become a breeze. Roland's unit would start to become pretty good after a while, at least he would be able to handle two or three units on his own. Also, Borus would start to not suck so much, and would start to consistently kill enemies (raising his "swing" skill is essential).
Once you get to that stage, you would need no help with major battles.
5) Make sure you choose the right enemies when dying.
After you reach above level 50, dying in the Amur plains becomes a problem, because you have become so strong. It is important to die in the Amur Plains to make sure everyone's levels carry over. If you proceed with the events and die, levels of those who are not in your party at that time will not carry over to your last save. Which means you would wate an entire level-gain cycle. Thus, you simply MUST die in the Amur plains to make this trick a success.
The following enemies appear in the Amur Plains--
1) Wild Boar
Excellent damage and hit rate. If it hits you while you are casting a spell, you are guranteed 100+ damage. He is the man.
2) Dark Hare
Good at lower levels, but after your MDEF gets high, his lightning spells only take time. Damage is not bad, but their hit rate is pathetic. Avoid at higher levels.
Attack only, and inferior to Wild Boar in all aspects. They come un large numbers usually, but if you can get a Wild Boar, just ignore the wolf.
4) Troll Dragon (Area Boss)
Very good due to its fire attack on everyone. At higher levels it may get hard hoever with the higher MDEFs.
They also appear in certain configurations-- 1) Wild Boar x1
2) Wild Board x2
3) Wild Boar, Dark Hare x2
3) Dark Hare x1
4) Dark Hare x2
5) Dark Hare x3
6) Dark Hare x1, Wolf x3
7) Wolf x1
8) Wolf x2
9) Wolf x3
10) Troll Dragon (very rare)
Out of the above, make Wild Boar x2 is the best you can get. As for the strategy--
When you are trying to die, you must not attack. The only way to do this in Suikoden 3 is to defend, especially when your buddy group is still intact. This is because, even if you are casting a long spell and can not attack, your buddy will still atttack and spoil your attempt to die. Thus, it may be necessary to spread out your team of four into three separate groups, ideally with Chris in one group, Roland and Salome in another, and Borus in the last. In that case, meke sure you have some sort of magic rune attached to everyone (after they are high enough levels to have empty slots), and DO NOT raise their skills. The intention is to make it possible for enemies to attack you while you are casting a spell. This allows enemies to hit you while you are defenseless.
If you are casting a spell that takes more than one round to complete, start over with the incantations after one round so you can keep yourself in perpetual defenselessness for maximum damage.
In the case of Borus, make sure he only uses his "Flame Amulet" spell, because if you use his "Sword of Rage" spell, he often ends up attacking after he complete the spell.
With all of those preparations, you will be able to get all these four characters to level 99. Which also means that other characters recruited by Chris who have starting levels that are influenced by those who recruit them (such as Watari, who joins at +2 of the recruiter's level, or Ayame, who is -1) would start off from level 99 or something sligtly below that. Thus, this tedious level gain process ends up being a level 99 trick for many other characters who do not have set levels at the time of joining.