Chameleon

Special Ability
Chameleon is able to freely change its element by going to its pet page. After you evolve it, Chameleon will count as the correct element for dungeon events regardless of the element you have made it.

Unlock
Chameleon is a special boss you will encounter in Depth 2 in the 5 specific element dungeon if your party items include at least 1 tier 3 mat for that dungeon (magic wood for forest, magic ore for scrapyard, etc) 'and' at least one pet of that element. It is around the difficulty of a Depth 2 Difficulty 2 boss. Once you defeat chameleon in a specific element it will no longer appear. Once you defeated all 5 you will you be able to recruit Chameleon as a pet. The strategy for each boss is about the same as the normal dungeon boss that appears. Have the ability to run each dungeon at D2-2 or D2-3 before attempting these fights.

Chameleon's element values change depending on the dungeon it is fought in. For example, Volcano Chameleon has 250 Fire and 50 for all other elements. Forest Chameleon has 250 Earth and 50 for all others. Etc. The exception is with Scrapyard Chameleon, who has 120 for all elements.

Evolving Details
All of the dungeons need to be done at D2 for 48 rooms, meaning no traps/events triggered causing you to lose any rooms or you will fail this requirement. Chameleon does not need to be in the dungeon to get credit added towards the evo. These dungeons will only start counting after you have unlocked Chameleon first and you can check which dungeons you still need by attempting to evo assuming you meet the other requirements.