Buena and Bueno behave as expected.
Buen is like bueno, but only if it's followed by a noun.
Malo and mala, likewise, are adjectives, but mal is an adverb! Hablar mal, etc. "Bien" is its counterpart.
"El mal" means evil, "el bien", good... Also, "Bondad" and "Maldad"
email me: stack (at) tilde.cafe