The fastest way to level up in Pokémon Scarlet involves several methods, each with its own advantages. Here are the most effective strategies:

1. **Hunting Chansey with Ham Sandwiches**
– **Step-by-Step Instructions:**
1. **Prepare Ham Sandwich Ingredients:** Buy ham, pickles, mustard, and mayonnaise.
2. **Make a Ham Sandwich:** Use the ingredients to make a Ham Sandwich. This will give you the Encounter Power: Normal buff, which increases the spawn rate of Normal-type Pokémon, including Chansey.
3. **Travel to North Province (Area Three):** Use Koraidon or Miraidon to travel to North Province (Area Three). This area is known for having high-level Chansey.
4. **Defeat Chansey:** Hunt and defeat Chansey in the area. Each Chansey defeated will give your main Pokémon around 5,000 XP, while other party members will receive 1,000-3,000 XP depending on their level.

2. **Participating in Tera Raid Battles**
– **Step-by-Step Instructions:**
1. **Unlock Tera Raids:** Clear the story and unlock Tera Raids by approaching glowing crystal chunks on the map.
2. **Join 5-Star or 6-Star Raids:** Participate in 5-Star or 6-Star Tera Raids for higher EXP rewards. These raids also offer Exp Candy XL or L as additional rewards.
3. **Earn EXP Candy:** Use Exp Candy XL or L to level up your Pokémon quickly. Exp Candy XL gives 30,000 EXP, while Exp Candy L gives 10,000 EXP.

3. **Using EXP Candy or Rare Candy**
– **Step-by-Step Instructions:**
1. **Acquire EXP Candy:** Find EXP Candy in Pokeballs scattered in the wild or as a prize in Tera Raid Battles.
2. **Apply Candy:** Use the EXP Candy on your low-level Pokémon to gain multiple levels at once. This is especially useful for high-level Pokémon that need a lot of EXP to level up.

### Additional Tips
– **Lucky Egg:** If your lead Pokémon is holding a Lucky Egg, it boosts EXP points earned by 50%.
– **Auto-Battle:** Once you’re at a higher level than the Chansey, you can auto-battle multiple Chansey to net a few hundred XP per battle.

By combining these methods, you can efficiently level up your Pokémon in Pokémon Scarlet.