You can't unlock Tabuu. It's kind of sad you can't. But, in Super Smash Bros. Brawl Melee
you can unlock Master Hand!
But, you can beat Tabuu of course! This is how to beat Tabuu in the next paragraph.
Tabuu tries to instantly KO everyone again, but Sonic leaps in and distracts
him. Pick your 6 dudes and get ready!
Tabuu warps around the stage constantly, making him difficult to hit. However,
he attacks in a semi-predictable order: he selects a move from group A, then a
move from group B, a move from group C, and finally uses a group D move. While
the first three attacks are random, he always uses the two group D moves in
alternation (that is, he never picks them twice in a row). Here they are:
Group A:
Grass Cutter: Forms a pink blade and swipes the ground with it. Easy to avoid,
just jump.
Shark Blade: Hangs in the air, produces a large blade, and flies horizontally
across the stage. Easy to avoid, just air dodge.
Golden Brackets: Take a pair of "brackets" and sweeps them along the stage.
If they grab you, you get thrown into the ground for a likely one-hit KO.
Very hard to dodge.
Group B:
Chain of Light: Takes a yellow rope, quickly grabs you, flings you around a
bit, and slam you into the ground. Very powerful attack, almost no time to
dodge.
Quark Glitter: Shines five or six points of light a cross the stage, which
quickly explode. KOs often.
Electro Field: Generates an electric field around himself that expands and
then shrinks. Not hard to avoid. Projectile bait.
Fury Swipes: Appears right in your face and slashes at you. Traps easily.
Dupli Fling: Sends copies of himself in all directions. High KO power. Explode
on contact with the ground, meaning you can dodge the thing itself but still
get hit by its shrapnel.
Group C:
Dragon Laser: Uses a large cannon-like device to shoot a beam along the
ground. Jump to avoid, but it lasts a while.
Bullet Rain: Appears near you and showers you with needles. Fires a large
KOing fireball at the end. The move sweeps while being used, so the only safe
spot is behind the enemy.
Triblade: Throws a spinning blade along the ground that acts like a boomerang
and makes two passes. Jump over it.
Group D:
Off Waves: A series of three stage-covering rings that do huge damage and an
instant KO. Sidestep dodging is the only way to reliably avoid them. Or, you
can use a mid-match character swapping move.
Giant Laser: Grows huge, appears at the side of the stage, and shoots a pair
of giant lasers across the stage, similar to Master Hand. Very easy to avoid;
just get right on the edge of the stage and wail at 'im.
Other:
Explosive Teleport: Sometimes, Tabuu decides to cause damage when he
teleports. This does significant knockback, so keep away if you can tell he's
doing it. I believe this happens more often at lower health, but I'm not sure.
After a move, Tabuu will warp to a spot and sit there for a few seconds. That's
your time to beat him up.