I actually have 3 ideas for Servants, so I'll just list them all in one comment.
1. Kraun (Berserker)
Servant Stats:
True Name: Kraun
Type: Heroic Spirit
Source: Original Mythology
Region: Europe
Alignment: Chaotic Good
Hidden Attribute: Earth
Armaments: None
Parameter: .
Strength: A+++
Endurance: EX
Agility: A+++
Mana: E-
Luck: C
Noble Phantasm: A+
Class Skills: .
Mad Enhancement: EX
Personal Skills: .
Monstrous Strength - A
Natural Monster - A++
Battle Continuation - EX
Beast Killer - A
Bravery - A
Noble Phantasm: .
Extinction of Beasts - Anti-Unit - A++ (EX against Beasts or Heroic Spirits that are part Beast)
A manifestation of Krauns desire to rid Earth of malevolent beasts and make the world a more peaceful place, his Noble Phantasm is a simple but lethal double strike with the bone-blades that protrude from his arms. Kraun will draw both of his arms back, leaving him vulnerable to frontal attacks, but as soon as his opponent takes the bait and comes within range, he swings both of his arms forward at the same time in upward arcs, tracing an "X" symbol in the air. If this attack lands, the target will be either instantly killed or severely wounded depending on the targets Luck Parameter, however, Beasts or Half-Beast Heroes will be immediately destroyed by this Noble Phantasm, even if they have A+ or higher Luck.
2. Zone (Saber)
Servant Stats:
True Name: Zone
Type: Heroic Spirit
Source: Original Mythology
Region: Asia
Alignment: Lawful Good
Hidden Attribute: Human
Armaments: The Key
Parameter: .
Strength: A+
Endurance: A
Agility: A+
Mana: B
Luck: B
Noble Phantasm: A+
Class Skills: .
Magic Resistance: A
Personal Skills: .
Mana Burst - A
Bravery - A
Beast Killer - A
Noble Phantasm: .
The Key - Anti-Army - A+
As the bearer of The Key, Zone has the ability to open portals to other realms at will. Her Noble Phantasm is triggered by thrusting the key into the ground and twisting as if she was opening a lock, by doing this she opens a portal to Hell and allows the Flames of Hell to pour freely onto the battlefield. This attack is capable of incinerating an entire army within seconds and the burn wounds inflicted by the hellfire are very difficult to heal, even for skilled Mages.
3. Slenderman (Caster)
Servant Stats:
True Name: Unknown
Type: Heroic Spirit
Source: Original Mythology
Region: Germany
Alignment: Chaotic Evil
Hidden Attribute: Beast
Armaments: None
Parameter: .
Strength: A
Endurance: B
Agility: A
Mana: EX
Luck: E
Noble Phantasm: A+
Class Skills: .
Magic Resistance: EX
Personal Skills: .
Monstrous Strength - A
Natural Monster - EX
Infinite Mana Supply - EX
Mana Burst (Flames) - A+
Manslayer - A+
Noble Phantasm: .
Welcome To My World - Reality Marble - EX
Embracing his origin as the German Legend of Der Ritter, Slenderman casts a Reality Marble over the surrounding area that transports him and his opponents to The Black Forest in Germany. Here, Slenderman gains a drastic boost in power due to being in his homeland and his legend being stronger there, the only way to escape this Reality Marble is to engage Slenderman in direct combat and break his concentration, which is incredibly difficult since he switches his battle strategy to fighting more like an Assassin than a Caster in this world.