Sokka, Tenacious Tactician

Prowess is a triggered ability. “Prowess” means “Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.”

If a creature has multiple instances of prowess, each triggers separately.

Menace is an evasion ability.

A creature with menace can’t be blocked except by two or more creatures. (See rule 509, “Declare Blockers Step.”)

Multiple instances of menace on the same creature are redundant.