European Spanish: Te echo muchísimo de menos. Latin American Spanish: Te extraño muchísimo. Missing someone is "echar de menos" in European Spanish and "extrañar" in Latin American Spanish. You can say "te echo mucho de menos" and "te extraño mucho" and it would be "I miss you a lot", but since muchísimo is more than mucho it could be translated as "badly" in this case. You can use other expressions meaning a lot, for example "te echo de menos una barbaridad", "te echo de menos un montón" and so on. Yo can also use other expressions, such as "ni te imaginas cuánto te echo de menos"

I would translate the sentence as: "Te echo demasiado de menos" Or "Te echo muchísimo de menos" Badly literally means "de mala manera" or "malamente" But "te echo de menos de mala manera" is something you don't actually use in spanish.

normalmente se dice te extraño mucho

in colloquial speaking we normally say: "te extraño demasiado"

Te extraño malamente, pero lo mas normal es te extraño mucho o demasiado o bastante y esto me provoca sentirme mal...