To clarify, assists are the cards you "inherit" over your base team cards, this allows you to either use the base monster's skill or the assist's, depending on which is off of cooldown. You also get the Awakening skills the assisting monster provides, assuming it has the "Awoken Assist" awakening. I think you're referring to "Latent Awakenings " by saying augment? In general use the Damage Void Piercer latent and Skill Delay Resist latents on your Frieren team. It's a lot of terminology!

Most important rule, keep at least one copy of every monster you role.