- Use type advantages. Wartortle is a Water-type Pokémon, which is strong against Electric-types like Raichu. Take advantage of this type advantage by using Water-type moves like Surf or Hydro Pump. Raichu also uses Water and Normal type attacks, so watch that it doesn't get the upper edge.
- Use status conditions. Wartortle can learn the move BubbleBeam that has a small chance of confusing the target. Confuse Ray (TM25) is another option for confusing the target. If you can confuse Raichu, it will randomly attack itself or its allies.
- Train your Wartortle. Make sure your Wartortle is at a high enough level to learn powerful Water-type moves like Surf or Hydro Pump. You can train your Wartortle by battling wild Pokémon or by using Rare Candies.
- Use items. Use potions to heal your Wartortle during the battle. You can also use status-healing items like an Antidote if Raichu poisons your Wartortle, an Awakening if you successfully confuse Raichu, or an X-Speed if you want Wartortle to strike first.
- Be patient. Defeating a level 24 Raichu with a level 16 Wartortle will be challenging, but it is possible. Be patient and use the strategies listed above. With some effort, you will be able to defeat Raichu and move on to the next challenge.