Deepwater Barracuda Charm in LakeIllOmen broken
 

I've charmed a deepwater Barracuda multiple times in the past and they come out on land with you as is normal. The problem is when I tell it to attack something, it doesn't - it just sits there. It can still get aggro'd by mobs but doesn't retaliate. When I break charm, it just goes back into the water and doesn't attack me.

Correct. Welcome to classic amphibious mob interaction.

Certain aquatic creatures would come out of water. Some would reset into the water if you stepped out. Deepwater barracudas are some of those.