How do you become a toad in Talisman?
It is hidden in the encounter section of the rules:


  Other times the encounters are hostile
  and attack the character, or even turn him into a slimy Toad!


You will remain a toad for three turns, unless:


  If a character is already a Toad and is turned into a Toad
  again (for example, as a result of the Random Spell), the character
  remains a Toad for three more turns starting from the
  second transformation.