How to beat a Malboro really easy:
Go in with the initiative junction and mug. Hit the Malboro, see if it steals- if it doesnt, run away!

Alternatively:
Junction Initiative to two characters, rinoa and someone else. Have the second character cast aura on Rinoa. Hope she uses invincible moon.

Use a holy war (refine the Laguna Card or Gilgamesh Card)

Win Malboro Cards- they all refine into Malboro tentacles.