Echo Knight multiclass damage calculations

Question

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.

Unleash Incarnation

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.

Divine Fury

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?

Answer 1

The answer to your question is in Unleash Incarnation.

you can make one additional melee attack from the echo's position.

You are making the attack. Anything that has an effect on attacks you make will also have an effect on the attacks from the echo's position. The only part that would be counter-intuitive is the fact Hammering Horns allows

you push it up to 10 feet away from you.

This references YOU, not your attacks location. So you would push the target away from your location, not away from the echo's location. Although I wouldn't fault a DM for changing this.

Similarly, any condition or limitation which references the attacker or defenders location may interact unusually. For example, if you read the prone condition:

An attack roll against the creature has advantage if the attacker is within 5 feet of the creature. Otherwise, the attack roll has disadvantage.

You are the making the attack, not the echo. So even though its counter intuitive, strictly speaking you would be at disadvantage on your melee attack if only your echo was within 5 feet of a prone target.

As before I wouldn't fault a DM for overruling this. Its just an unusual corner case.