Different combos do different things.

You have to use EXACTLY the cards in the combo and no other cards on your turn and you have to use the cards in order. If you want to use your dud bomb to upgrade fire yell I to fire yell II use one dud bomb then two fire yell I. It should register a combo and at the end of the battle one of your items will be fire yell II. If you do two sword attacks then a dud bomb and follow up with two fire yell I, you won't get squat. For each of the combos you have to do the combination exactly as it hints or you don't get the new item at the end of the fight.

Wasabi needs a dark place to mature at it's earliest stage, so you use the Wasabi then the spell Dark (any strength) to advance it. The second stage needs fresh water, so you use the new card with a water (I think it has to be the item not the spell) and you get the mature Wasabi which is a powerful aid in battle.

Also, you can use some items for defensive purposes, with these items if there is a combo that you form with them you will yield the same item as you would if you used them when you had your attack phase. You have to use each magnus in order and NO OTHERS to preform the combo and get your prize. I cannot stress this enough. If you want the best items in the game for your characters some of them have to be earned through item prize combos. Follow the breadcrumbs.

If you're talking about number combos, there's a faq I saw on them. They either go, 1-9 (straight), 9-1 (straight) or two of a kind (1, 1) or better (1, 1, 1) or even better (1, 1, 1, 4, 4). The straights have to be in numerical order, don't have to be a certain length or start on a certain number and add to attack or defense a lot more than two of a kind, three of a kind, four of a kind, etc... But you will always get the matching bonus as long as there isn't an odd card out. If you as a guardian spirit are more in tune with what your bonded human is feeling (through the responses you give) it increases the likelihood of the 6 guardian spirit attacks activating during an attack round.

(I apologize for being unable to give exact names, my fiancee is borrowing my copy of Baten Kaitos)

you thuck, you make combos by randomly combining cards, its just all by chance if u get a combo, bcoz i have used marvelous sword, silver sword, and 2 rays of truth and got demon of the darkness. so just randomly combine crap you ninny.o also, the "you dead" thing isnt true, bcoz i make like no combos and dont die. so that guy u also thuck.

Man why did you buy this game.If you can't make combos you dead.If you mean special combos u gotta figure them out yourself .If u mean when those really powerful cards appear,then I'm not sure if you gotta make some really long combos or your gardian spirit gives them to u but I'm sure that your guardian spirit gives them to u but the problem is how.Haven't u noticed that only Kalas can do these atacks and after u form a bond with Xhela she does them.Plus they even tell you that your guardian spirit gives them to u but they don't telol you how.