Formal:
* Très mal: This is the most literal and neutral translation.
* Extrêmement mal: This emphasizes the severity of the situation.
* Horriblement: This implies something is truly awful.
Informal:
* Super mal: This is a more colloquial way to say "very badly."
* Dégueulassement: This is a slang term that means "disgustingly."
For specific situations:
* Très difficilement: "Very difficultly"
* Très douloureusement: "Very painfully"
* Très maladroitement: "Very clumsily"
The best option for you will depend on the specific context and your desired level of formality.