I am currently working on a new character concept for an upcoming game and was unsure about what damages the Echo Knight's echo would actually be able to do.
For this scenario, the build will be a Minotaur Zealot Barbarian 5 / Echo Knight Fighter 3 with the Great Weapon Fighting fighting style and Great Weapon Master feat.
You can heighten your echo's fury. Whenever you take the Attack action, you can make one additional melee attack from the echo's position.
Starting when you choose this path at 3rd level, you can channel divine fury into your weapon strikes. While you’re raging, the first creature you hit on each of your turns with a weapon attack takes extra damage equal to 1d6 + half your barbarian level. The extra damage is necrotic or radiant; you choose the type of damage when you gain this feature.
Great Weapon Master
You’ve learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You gain the following benefits: On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action. Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.
Great Weapon Fighting
When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2. The weapon must have the two-handed or versatile property for you to gain this benefit.
When the character makes the attacks from the Echo's location do all the extra attack damage benefits apply to the attacks?