Solution: Well, nobody got this one in about 4 or 5 days, and rather than hold up the entire thread with one puzzle I'm going to reveal the solution. If you still want to solve it on your own, I put it in secret tags... you don't have to look, I won't tell anyone.
Click here to view the secret text
×When you pair up the animals, you get:
Blue frogs making a diamond, with the letters WAY
Yellow fish making a spade, with the letters TRUD
Magenta ...somethings... making a heart, with the letters FL and the unknown
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×Since everything has to be used exactly once, and the animals were used to create the shapes, this leaves you with:
Blue Diamond WAY
Yellow Spade TRUD
Magenta Heart FL ?
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×I wouldn't have mentioned in the hint the difference between magenta and pink unless it was relevant to solving the puzzle. Taking the first letters of the colours and shapes and anagraming them with the letters, you get:
BAWDY
STURDY
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×...that's two adjectives (descriptive words... clue 5) An adjective that uses the letters MHFL is HARMFUL, so the missing letters are ARU (or any other letters that can anagram with MHFL to give an adjective).
Now, before anyone accuses me of creating an unreasonably difficult puzzle, here's the
much more sadistic puzzle I modified in order to create mine:

The solutions to this puzzle and mine are only in the most tenuous way similar, in that both solutions require you to make the shapes out of the animals. If anyone can solve this original version, I'll be very, very impressed... I might even give you a square or two from the prize box. It's not an official puzzle for this thread though, so no hints will be forthcoming for it.
As for this puzzle, well the square for it can't go unused; it will be added to the reward for the next puzzle, meaning whoever solves the next puzzle will get two picks from the prize box instead of just one!
Clue to follow!
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Deploy the... I think it's a yellow button... it's usually flashing... it makes the engines go... WHOOSH!