Version 1.2.0 update:
Added Enkidu servant (on Echo):

Enkidu

• Ability1(shift)
  Chains of Heaven extend :
  Shoot a chain forward that damages enemies that come in contact with it or are very close to it.

• Ability2(E)
  Chaingun :
  Fire consecutive chains forward that damage enemies hit by them or close to their impact point.
  The ability consumes ultimate charge to fire more than one chain.
  You can fire a maximum number of 10 consecutive chains in one use of the ability.
  
  Tech: The closer the final destination of the chains is to you the faster you will shoot them one after another.
  If you aim at the sky while using the ability you will have to wait until it reaches it's final destination until you can fire another one.

• RightClick:
  Fly forward.
  Tech: Press space to lock/unlock your position in air.

• Ultimate
  Enuma Elish:
  Create a growing yellow sphere that damages enemies inside of it.
  If an enemy is damaged 3 times by this area he will get stunned(rooted) for around 4 seconds.
  (totally immovable)

Description:
FGO:Arena is a 3 vs 3 elimination gamemode where you can choose from up to 50 servants , most of them inspired from the Fate Type Moon universe.

The game has one round and the rules are the normal elimination ones (with a capture point at the end).
Every character has custom abilities and ultimate.

Ab1 (ability one) is the standard overwatch "shift" key.
Ab2 (ability two) is the standard overwatch "E" key.

Every ability is explained left-top of the player's screen after he becomes the servant he wants.

To become a servant you can scroll through the available servants list a hero contains by using the right click and left click mouse buttons. Alternatively the player can just leave the spawn area and a random one will be assigned to him.

The game has a high skill curve because of the number of playable characters and abilities to learn.
If anybody thinks a hero is too strong or needs more in depth explanations of his abilities please tell me in the comments or anywhere you can find me (you can throw your rage at me, I'm okay with it).

This post will be updated soon with a list of all the servants and their abilities. And I will make a trailer video later this month.
P.S.: The gamemode is one round only because it crashes starting second round. If anybody manages to fix the crash bug please inform me and I will make it playable for multiple rounds.