To add something unnecessary that spoils or detracts from the original; to gild the lily.
彼の説明は十分だったのに、余計なことを言って画蛇添足になった。
His explanation was sufficient, but he said extra things and ruined it by adding unnecessary details.
プレゼンのスライドにアニメーションを入れすぎて、逆に画蛇添足になってしまった。
He added too many animations to the presentation slides and they became an unnecessary embellishment.
細かい修正はいいが、もう画蛇添足はやめよう。
Minor edits are fine, but let's stop adding unnecessary extras.