Waddle Dee is the easiest competitor in the game. Like he tells you, he'd rather just take a walk then compete. Actually his level is like the training level, and will show you how to move your pieces and such. You shouldn't have any problems with him.

Kirby: Hi, Waddle Dee! Are you ready?!?
Waddle Dee: Umm, can we just walk together? The forest scares me...
Kirby: Sorry, rules are rules!

Bronto Burt's bark is worse then his bite. He is nothing but a bully and poses no big threat. You should have great ease with sliding right by this guy.

Bronto Burt: Ah HA!!! I have found my next victim!!
Kirby: Bronto Burt you bully, the pleasure will be all mine.
Bronto Burt: Shut up and play!

Waddle Doo is mad at you for picking on Waddle Dee, but he is not much harder than Waddle Dee himself. He is also the end of the Learning Stage, so after you beat him you will have to start again.

Waddle Doo: You did not treat Waddle Dee with respect... Now I, Waddle Doo will repay you in kind!
Kirby: I don't think so!!

After you beat Waddle Doo, the screen comes up with King Dedede telling you to try the harder levels.

King Dedede: Congratulations! You are a fast learner. I underestimated your skill... MAYBE!

King Dedede: Now hurry through the forest and join us at the Dream Fountain for the serious competition.

Poppy is the beginning boss of the Normal Level, and is definitely more of a challenge than Waddle Doo. While his goal is to give you a bomb sandwich, you will probably beat him easily.

Poppy: Hi, Kirby! Want a bomb sandwich?
Kirby: I'll breathe in your pathetic bombs and send them
right back at you!
Poppy: Stalemate... Okay, let's compete in a quick game of Avalanche!

Whispy is back again and this time he actually takes a spot besides Level 1 in a game. However, although he may be a challenge at first he can easily be beaten sooner or later. Just hang in there.

Whispy: Please don't treat on my roots, it would not be a wise decision.
Kirby: I feel like some apple pie!

After Kirby teases Kabu as being a boulder, Kabu shows he can hold his own. In this battle you may have a little difficulty, but the later levels will make this one look easy.

Kirby: Who blocked the path with this boulder?
Kabu: Your road to glory ends here.
Kirby: OH!! Hi Kabu, are you ready for a game of Avalanche?
 

This level will move a lot faster than the previous, and you may have trouble at first keeping up. But there will be no trouble "sweeping" broom hatter up.

BH: Oh what a mess! Must I clean up this entire forest?
Kirby: I'd worry more about cleaning up your Avalanche skills first.
BH: Dush, dust, sweep... Huh?!??

Squishy is also fast, and keeps in the game very well. Consistence and fast pace will beat him.

Squishy: I know what your dream is! But King Dedede was saying-
Kirby: Go meddle in someone else's affairs, Squishy I've got to get to
the Dream Fountain.
Squishy: An eight-armed Avalanche for you then, Kirby!

Well they are back, and this time are quite a battle! This one you may have a lot of trouble with. They are a long match, but just keep at it. If you are using an emulator, the save states will be very handy.

Kirby: To get this far you must haev a-MAZE-ing skill Tee hee hee!!
LandL: Oh yea? Try and figure your way out of this!
 

Bugzzy is a little challenge, but not as much as Lololo and Lalala was. Again, just keep the pace and pay attention to each piece as it falls, and you should do fine.

Bugzy: ROOAAAAAAARRR!!!!!
Kirby: Oh, I'm soooo scared
 

This is another challenging match, and you may also have a tiny problem with him. Just try and go fast.

Paint Roller: Let me paint you a lovely portrait...
Kirby: Oh, how sweet of yo-
Paint Roller: ... of you losing to me, HA HA HA!
Kirby: Paint Roller, you are the meanest art student I've ever met.
Paint Roller: Student? HA! I am the MASTER!!
 

Heavy Mole is a good fight, however if you've gotten this far you probably won't have to much of a problem with him.

Heavy Mole: I am Heavy Mole, watch while I undermine your precious dream!!
Kirby: You are sneaky, but I will not be distracted by your under-handed tactics.
 

They are back again in this game, and pose a big challenge. With their
"dual" power you will find this fight pretty aggressive. Just try to start with small avalanches at first, don't try to set up anything big, chances are they will block it before you can anyway.

Shine and Bright: We rule both the night and the day!
Shine and Bright: This leaves no time for you Kirby! Be gone!!
Kirby: I thrive at dusk and at dawn! I'll have you two fighting before the day is done.

Kracko keeps the pace very fast and will probably bomb you with boulders. Just keep knocking them down and starting with small avalanches like you did with Mr. Shine and Mr. Bright.

Kracko: KRRR-RACKK!!!! Dance to my deadly music, or fry like a moth! HA HA!!
Kirby: You couldn't hit a barn sized lightning rod, Kracko!

The level before the last, and Meta Knight has certainly earned his place here. The game moves faster, but Meta Knight will pile on the boulders and move with great accuracy. Just keep going, once you stack him up high, he starts to sway.

Meta Knight: None shall pass! En garde, Kirby!
Kirby: But I have no sword!?!
Meta Knight: Oh, you're so right... Then Avalanche it is, ha ha ha ha!!!

With the speed and King Dedede's knack at piecing together avalanches, this is the ultimate challenge. While his thundering hammer may be intimidating, just keep going and try to stack him up high. Just watch out for his boulders, you'll be seeing them a lot.

King Dedede: Kirby!! Your dream has carried you far but here it ends.
King Dedede: The Dream Fountain Cup will be mine!!
Kirby: Welcome King Dedede. And good luck to you too.