• IronIngot
  makes soldier vastly resistant to knockback, increases knockback dealt to others, both effects neutralized vs another iron ingot user
• Brick
  makes soldier extremely slow and less willing to move, will use ranged attacks if available before melee
• String
  makes soldier resist all damage from one explosion
• Cactus
  75% chance to negate burn time, halves total burn time otherwise
• NetherBrick
  gives burn time to any soldier that attacks nether brick user with unarmed attacks

Could have sworn the iron ingot also made soldiers unable to use mounts. Speaking of, I do hope you plan to add more than just the horses back. The lizards and turtles were awesome.