Tidus/Gameplay

Tidus, Selphie, and Wakka are Sora's three friends on Destiny Islands, and are a set of optional bosses found in Kingdom Hearts. They ask Sora to have practice fights with them on the first and second days on the island. After defeating each of them individually, Sora can ask to fight all of them simultaneously. These three are an optional boss and you do not have to face them.

Kingdom Hearts
Tidus is a little bit tougher than Selphie or Wakka, but the match is simple. In a similar style to Sora, Tidus fights using a stick. The best way to defeat him is by dodging his strong attacks and trying to jump behind him. While still in the air attack him with an aerial combo. Also, to get some Tech Points, try parrying his attacks by striking at the same time he swings and you will stun Tidus, allowing you to get in one or two combos without interruption. After a few rounds of this you'll win. He also seems to tire out every once in a while; this leaves him open for a combo.
 * Tidus

Selphie fights with a jump-rope as a toy version of sorts to her original nunchucks. During the fight, if Sora manages to deflect her jump-rope, he earns 1 Tech Point. If the jump rope hits Selphie's head in the process, Sora gains an extra Tech Point. It should be noted, though, that if Sora fights only by deflecting Selphie's jump rope, her HP will be reduced to 1 and will not decrease any further, making it a good way for Sora to gain experience before dealing the final blow. Be careful in the battle as it is a bit hard to spot her jumping rope and she could land an attack on you if you're not careful. If you're fighting her alone, lock on to her and you'll be able to finish her in no time. Also remember to make sure most her hits dont have contact with you cause most of the time they will stun you.
 * Selphie

Depending on your timing, Wakka is the easiest character on the island to beat and a good way to gain experience. During the fight, if you are far from Wakka, then he will throw the ball at you at a normal pace. If you can hit the ball at the right time, it will deflect to Wakka and you will gain 1 tech points. Occasionally he will launch a faster stronger ball (he will jump and yell "Take this!"), and if you hit it you will receive 2 tech points. This is the best time to strike as he is basically defenseless but, watch out for the ball he will throw randomly while he is stunned. Take this time to use ground and aerial combos on him. In close range combat, he will do a spin attack on you which is fast and hard to block. Note: If you hit Wakka back with his own ball, he will be stunned and confused for a short period of time, giving you time to strike.
 * Wakka