to make matters worse; on top of that; what's more
Adds an additional negative or undesirable point to a situation. Often used when listing complaints or unfortunate circumstances.
It started raining. On top of that, I forgot my umbrella.
He was late. What's more, he forgot his homework.
その上 is neutral and can add either positive or negative information, whereas おまけに almost always adds a further negative or unwelcome fact.
しかも is a slightly more formal connector that can introduce positive or negative additions, while おまけに leans toward complaining about extra bad news.
それに is a casual, neutral way to add another point, whereas おまけに specifically emphasizes that the added point makes things worse.
おまけに simply adds an extra fact on top of what was said, whereas それどころか implies the added fact contradicts or far exceeds the first statement.
おまけに is a casual, conversational way to add an extra (often unwelcome) point, while そればかりか is a bit more formal-sounding and can be used in writing as well.
Applies to each form listed below
Rare kanji form; not recommended for learners.
Rare kanji form with honorific prefix; not recommended for learners.
Derived from おまけ (bonus, extra) + に (particle), literally 'as a bonus'. The negative nuance developed from the idea of an unwanted extra.