From the Super Mario Wiki
The Gold Koopeleon is a rare variety of Koopeleon, the Koopa Troopa chameleon. In Mario & Luigi: Partners in Time, Gold Koopeleons live in the Thwomp Caverns, the interior of the Thwomp Volcano. Gold Koopeleons, as their name implies, resemble regular Koopeleons, except they are gold, shiny and flashing. Also their attacks are faster and much stronger.
As the Koopeleon, Gold Koopeleons have the ability to turn invisible. Unlike Koopaleons, however, Gold Koopeleons turn invisible to hide from attackers therefore meaning the player cannot attack them while they're in this state. Gold Koopeleons give many Gold Coins and plenty of EXP. Additionally, although Gold Koopeleons have max defense, they also have low HP.
Unlike Koopeleons, Gold Koopeleons tend to flee rather than fight. However, if a Gold Koopeleon decides to fight, it may use two attacks in battle. First, the Gold Koopeleon may change color to blend into its surroundings (making it look like it has turned invisible) and attempt to run into the attacker. This attack can be countered by jumping. Secondly, a Gold Koopeleon may run up to Mario or Luigi and hit him with its tongue. Again, this attack can be dodged by jumping. Sometimes, the Gold Koopeleon performs multiple tongue strikes, meaning the Mario Bros. have to jump multiple times to avoid taking damage.
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