There are six different types of Elements for Sidekicks:

• Fire
• Light
• Nature
• Shadow
• Water
• Prismatic

The Elements on the Sidekicks provide 50% bonus damage on certain bosses:

• Monster King (Normal) is weak to Shadow 
• Mildred (Nature) is weak to Fire 
• Fluffy (Toxic) is weak to Nature 
• Monster Queen (Shadow) is weak to Light
• Spike (Ice) is weak to Fire 
• Ice Queen (Ice) is weak to Fire 

In Boss Raids, certain Boss enhancements will change the weakness type:

• Frozen (Ice) is weak to Fire
• Molten (Fire) is weak to Water 
• Toxic (Toxic) is weak to Nature 
• Dark (Shadow) is weak to Light 
• Blinding (Light) is weak to Shadow 
• of Doom (Shadow) is weak to Light 
• from Hell (Fire) is weak to Water
• The Prismatic Element is strong against all Elements, so it will provide a 50% bonus damage on all bosses.