Instructions
Give Shuckle an EXP Share item to hold and let stronger Pokemon collect experience for it. EXP Share pulls experience points from the Pokemon in battle to the creature that is holding the item. Have your strongest Pokemon take on powerful wild Pokemon and strong Trainers with Shuckle in your party holding the EXP Share to raise its experience level very quickly.
Feed Shuckle a Rare Candy to instantly increase its experience level by one. These items are aptly named, as they are difficult to come by, but the effect they have on Pokemon is invaluable.
Trade Shuckle to another Nintendo DS game, and trade it back to "Pokemon Platinum." Traded Pokemon grow faster than monsters caught in your game. The extra experience Shuckle will earn with every battle adds up fast.
Drop off Shuckle at the Day Care center in Solaceon Town. Every step you take while Shuckle stays at the Day Care location, it gains experience points. Dropping off Shuckle, going on an extended adventure and returning will have a huge positive effect on Shuckle's growth.
Build a battle strategy around Shuckle's natural abilities to win Pokemon battles. Since Shuckle can take a lot of punishment due to its extremely thick shell, teach it attacks that hurt the opponent over time. Bide, Constrict, Rest, and Power Trick are all artful attacks that Shuckle can use effectively. Win many high-level Pokemon battles to gain large amounts of experience to grow Shuckle.