From Bulbapedia, the community-driven Pokémon encyclopedia.
When you enter the Meadow Zone, the first zone you will ever visit (not counting the PokéPark Entrance) the game gives a very detailed-media "explanation". It shows you all of the features of the Meadow Zone, which mainly consist of grass, trees, and flowers, not to mention the sun always shining brightly. As such, this is an ideal spot for any Grass or Bug type.
After this explanation is over, you see two Speech Bubbles over two Pokémon. When you walk closer (but not too close so they can talk to you) you'll notice it's the Buneary from earlier and...could it be? Is that really Chikorita, or are you just having illusions?
It truly is Chikorita. Walk close enough this time so they can talk to you. Apparently, they're chatting animatedly, and don't seem to notice you until Buneary decides to turn around. Chikorita, noticing this, turns around. As you are both friends, naturally, she is very happy to see you. Buneary is also very happy for the two of you being reunited, which the game notes. Chikorita mentions she also got a Pal Pad. Buneary then says something about Attractions, which are things you play at each zone. Every time you come to the PokéPark, you can never miss the Attractions!
After this is done, head over to another Pokémon with a speech bubble, a Bulbasaur. He's sitting next to a signboard, which says something about playing Bulbasaur's Daring Dash and how you need five berries to play. Talk to him.
He's extremely bored, and has had no customer in a while. He wonders (and hopes) if you want to play the Attractions, perhaps thinking you are new to the PokéPark. You will then accept, causing Bulbasaur to get extremely happy. He's so happy, in fact, that he allows you to play, free of charge!
Bulbasaur's Daring Dash
As the first Attraction, very easy. All you need to do is shake the Wii Remote as fast as you can in order to try to secure first place. As this is your first time around, there will be a goal, which you need to get around that time so you can complete this. All other times, however, it will only be Bonuses, which gives you a 100 berries if you can complete the Attraction within the Bonus Time Limit.
Pokémon who can Play
After completing this, you will see Pikachu cheering, and then the game will leave that.
Sky Prism Piece #1
Bulbasaur is very happy that there is finally a customer, as he has had no one in ages. Then he pulls out something shiny with some aura flowing around it. It is a Sky Prism Piece. Bulbasaur said that, in a dream, a strange Pokémon talked to him, saying that whoever completes this Attraction (after friendship fell) should get this. The game then notes about your success.
Chikorita, it seems, is suddenly at your side, and Bulbasaur is there too, wondering what's happening. Suddenly, a Treecko and a Mankey come over, looking quite stern. Treecko knows that you've played the Attraction, which Treecko says you're not allowed to do. Chikorita defends you, saying there was no point in having Attractions if no one was allowed to play them.
The two of them ignore Chikorita and Mankey says they'll have to hand over Bulbasaur to Venusaur since he let you play the Attraction. Bulbasaur, it seems, is very scared of his final form and pleads with them, making Chikorita stand up to them once more.
After this, they can't ignore Chikorita any longer. This causes Chikorita to be carried away by Mankey, being lead to Venusaur by Treecko.
Buneary sees this, and gets extremely worried for Chikorita, as they seemed to have become friends over their conversation. She is also very sad since she thinks it's her fault for telling you about the Attractions. Bulbasaur is slightly worried about Chikorita too, but he is also concerned about getting thrown to Venusaur...which was probably what was happening to Chikorita.
So, both of them simultaneously ask you to save Chikorita.
When you try to go across the bridge to save Chikorita, Treecko is guarding it and won't let you across the bridge no matter how hard you try. Although...Treecko says that if a Pokémon called Turtwig can get the Bonus in Bulbasaur's Daring Dash, then he will let you across the bridge. Treecko is doubtful, however--since, according to him, Turtwig is very slow!
Go and look for Turtwig. You'll see a Speech Bubble hovering over a rather large patch of grass, so go and investigate. It turns out to be...Turtwig! Turtwig, by any means, refuses to let you force him into doing Bulbasaur's Daring Dash. However, he said he will go and do it if you defeat him in a Chase!
Since Turtwig's speed isn't too fast, and your speed is decent, this should be quite easy. After you finish, he is still brooding on how he still feels like he is flying to the air. Because you defeated him in a Skill Game, he is now your friend, and he gives you some berries.
Go back to Bulbasaur and talk to him. Bulbasaur explains that, if you make a friend, that friend may be able to play Attractions. This time, you have to pay, but it's only five berries, so not a big deal.
No Goal Time
This time around, there is no Goal Time, and this time, unlike with Pikachu, you have to get the Bonus Award if you want to get across that bridge, like Treecko said. Shake Wii Remote as fast as you could, nothing else to it.
After getting the bonus, you'll gain a hundred berries. Go and talk to Treecko. He seems to have a jealous look, but he denies it and says he "never really liked that Attraction anyway". He then stops guarding the bridge, allowing you to go and advance in your search for Chikorita.
After crossing the bridge, there is yet another hurdle--Mankey. How could we forget? Mankey is going to have a Battle with you, a new Skill Game.
Like in main series battles, both of you have HP. In this case, Mankey has two sections of HP, as well as you. You can gain more HP via Bibarel at the Meeting Place, and learn a new attack called Iron Tail via Primeape at the Meeting Place. You can also make your Quick Attack faster with Ponyta at the Meeting Place, and power up your Thunderbolt with Electabuzz at the Meeting Place, which is the first thing you can do.
However, you don't have those things yet, and so here is the current battle status:
After defeating Mankey, he'll let you go on, surprised that he lost, though he'll become your friend.
Head on over to the left path, which will lead you to Venusaur. Go to a Pokémon called Croagunk, the gatekeeper. He wonders why you're here, and once he finds out that you're here to see Venusaur, you'll have to make a deal with him first. Apparently you'll have to give him 200 berries, which, if you got Pikachu's and Turtwig's bonus, as well as picking up berries you find in boxes, then you'll have enough berries. He drains all of the berries, and then realizes you're noble, so gives you 170 of them back.
Then, he opens the gate.
Once you're there, you'll see Venusaur having a Speech Bubble over his head. Go and talk to him.
He scolds you for playing the Attractions, and Chikorita defends you again, saying again that there is no point in having Attractions if no one is going to play them. He gets extremely upset at her, and refuses to stop holding her hostage. However, he does say he's going to change back the rules of the Meadow Zone if you beat his caretakers, which are Croagunk and a Spearow. However, he trusts them, and doubts you'll beat them!
Go outside of his "lair" and talk to Croagunk, who then realizes you need to battle him. Croagunk laughs under his breath, saying it's fun to play the villain. He also tells you a tip in battle--when an attack is going to be shot at you, quickly press either "left" of the Control Pad or "right" of the Control pad to dodge. You then start your battle.
After defeating him, Croagunk says that you could have gone easy on him, as he even gave you a tip to dodge his attacks, although you claim you weren't doing your best.
Don't go to the right path, where another Spearow is, but go to a place where you see an odd number of stumps. There is the Spearow that you are looking for, who is bragging about how much Venusaur trusts him. He's not going to be doing a battle or a chase, but is instead doing a new Skill Game called Obstacle Hop.
Obstacle Hop is a Skill Game where jump on various objects to reach the Pokémon who challenged you. There is a very generous time limit. If you fall off, you'll start back at the beginning. In later and harder ones, Pokémon may send attacks at you.
Once you beat Obstacle Hop, Spearow is very surprised. Return to Venusaur.
Venusaur's Vine Swing
Venusaur is very surprised that you beat Croagunk and Spearow, but still refuses to give back Chikorita and reunite the PokéPark. Chikorita gets very upset, saying that she can't be held hostage forever. This causes Venusaur to get slightly embarrassed and say that, if you want to overcome the final hurdle and get Chikorita back, as well as have Venusaur reunite the PokéPark, is do Venusaur's Vine Swing.
Venusaur's Vine Swing is an Attraction where the Wii Remote is held vertically. Swing hard and press B to get the required goal/Bonus. If you get the bonus, Venusaur will give off petals from the flower on his back!
Pokémon who can Play
Venusaur gets surprised but happy that you completed the Attraction, and gives you a Sky Prism Piece, marking your second one. Chikorita gets happy, and asks whether or not Venusaur is going to reunite the PokéPark. Venusaur says he'll let Chikorita go, and reunite the PokéPark, although you have to send the message to the next Zone Keeper, Empoleon.
This is a list of Pokémon you can befriend in this zone.