What, when you need it you throw it away,
but when you don't need it you take it back.

Answer

An anchor

I am the highest rank
Unless you use the first
I am full, never blank
Sometimes I make you burst

I am surely one of a kind
The ruler of a formal wear
A man of wisdom you might find
In your hand I'm very fair

I have three good friends
All with swords in their hands
Our bond never ends
But I am different in thy lands

What am I?

Hint

The title is somewhat of a hint.

You also might Play with me.
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Answer

King of Diamonds

At large in a pond, attract mass in the ring
Find me in circus, see me in the zoo
People think I'm your average pink thing
Yet we know that's not exactly true
When it comes to balancing
You know whom to bestow the crown to

Hint

On shellfishes I mainly feast
But open mouth is for all; humans or jungle beasts
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Answer

A flamingo.

Many are pink, but healthier flamingos should be red, showing that they are not famished (have enough carotenic food) and bills (baby flamingos) are white.

The one in the circus is the ring/hoop that is on fire where trained animals (usually lions)/ human do tricks by jumping in/through.

---> Flaming "O"

Either way, both flamingos and the circus trick show exceptionally good balance. The bird sleeps on one leg to preserve body heat, and you need to practice hard and be really skilled to (train animals to) do the tricks.