Limpness; a state of being flabby or lacking firmness (the condition of being soft and floppy).
風船から空気が抜けて、ふにゃふにゃになった。
The balloon lost air and became limp and floppy.
朝起きたら枕がふにゃふにゃだった。
When I woke up, the pillow was all soft and flattened.
Soft; limp; flabby — describing something lacking firmness or structure.
そのマットレスは古くてふにゃふにゃだ。
That mattress is old and saggy.
ふにゃふにゃの髪の毛をブラシで整えた。
I smoothed my limp hair with a brush.
寒くて手がふにゃふにゃになった。
My hands went limp from the cold.
Mumbling; speaking unclearly (often as if with food in one's mouth); indistinct muttering.
彼は口にパンを入れたままふにゃふにゃ言った。
He mumbled something with bread in his mouth.
疲れているのか、返事がふにゃふにゃして聞き取りにくい。
Maybe he's tired — his responses are mumbling and hard to understand.