Pokéblocks, they are made from Berries and they raise certain stats by an amount determined not only by Level and Feel but of the Pokémon's Nature. Each Nature (except 5) Have a Taste They Like more than normal and a taste they dislike. The more they like it, the better the effect of the Pokéblock. If they like it, it takes extra effect. If they do not mind its a normal effect. If they hate it then it wont work well...so when you're training a Pokémon For a Contest make sure it's Nature goes with the Stat you're trying to raise. Be sure to consult the Pokéblock List and Berry List to get the perfect Berry and Pokéblock:

Nature Favourite Taste Hated Taste
Hardy None None
Lonely Spicy (Cool) Sour (Tough)
Adamant Spicy (Cool) Dry (Beauty)
Naughty Spicy (Cool) Bitter (Smart)
Brave Spicy (Cool) Sweet (Cute)
Bold Sour (Tough) Spicy (Cool)
Docile None None
Impish Sour (Tough) Dry (Beauty)
Lax Sour (Tough) Bitter (Smart)
Relaxed Sour (Tough) Sweet (Cute)
Modest Dry (Beauty) Spicy (Cool)
Mild Dry (Beauty) Sour (Tough)
Bashful None None
Rash Dry (Beauty) Bitter (Smart)
Quiet Dry (Beauty) Sweet (Cute)
Calm Bitter (Smart) Spicy (Cool)
Gentle Bitter (Smart) Sour (Tough)
Careful Bitter (Smart) Dry (Beauty)
Quirky None None
Sassy Bitter (Smart) Sweet (Cute)
Timid Sweet (Cute) Spicy (Cool)
Hasty Sweet (Cute) Sour (Tough)
Jolly Sweet (Cute) Dry (Beauty)
Naďve Sweet (Cute) Bitter (Smart)
Serious None None
 
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