[@vancexentan]
If Loki allows it, Caster can turn the fight with his Personal Abilities and see what is the Raid Boss' health. With assistance provided by having the two defending servants be given attack and defending options from Caster. With that, maybe we can corner the mystery tank servant and win this encounter. So, I'm ambitiously down for fighting the mystery servant if my partner allows it. 

<So basically a 3 v 1>

[hr]

On Rider's end, I will dispatch the two servants and cheese the other servant if possible. So, no fun on that end :P