From the Super Mario Wiki
The Gold Koopeleon is an enemy that appears in Mario & Luigi: Partners in Time, where it is found in the Thwomp Caverns. They are a shining golden variant of the regular Koopeleon. Like their base counterparts, Gold Koopeleons have the ability to turn nearly invisible, but will flee from Mario, Luigi and their baby counterparts in the overworld.
Gold Koopeleons have low HP, but maximum DEF, and tend to flee from battle rather than fight. When they do not opt to flee they use the same attacks as regular Koopeleons: they can blend into their surroundings and attempt to ram into one of the brothers, who can counter by jumping. Gold Koopeleons can also run up to Mario, Luigi, or their baby selves and attack them with their tongue, and may do so multiple times; this attack must also be dodged by jumping which if not, it may cause the trip status effect. Gold Koopeleons give plenty of coins and EXP points if the Mario Bros. and their baby selves can defeat them in time.
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