I want to try to make a character of each class that can bring him down, but obviously it is *much* easier for some classes than others. Without having actually made them all, I'm considering the degree of difficulty for each class to be something like (from easiest to hardest) Devastator, Librarian (since it doesn't have a collar of khorne), Techmarine, Tactical Marine, Assault Marine, Apothecary. Going to go from easiest to hardest, so without further ado, here is the obvious choice, the Devastator Marine
Imperial Fist Devastator Marine (Immovable Warrior)
WS - BS 70 (3200 XP) Str - T - Agi 60 (2250) Per - WP - Fel -
Skills n / a
Talents: Eye of Vengeance (1000), Hip Shooting (500), Marksman (500), Rapid Reload (500), Signature Wargear (Master) Lascannon (1000), Signature Wargear (Hero) Master Crafted Lascannon (1500)
Wargear: Mk VI Corvus Armor, armor history: n/a; Master Crafted Lascannon; Astartes Targeter (25)
Distinctions: Master of Arms (Felling)
Totals: Spent XP: 10,450; Requisition used: 25; Distinctions Needed: 1;
The Battle: It does not matter who goes first. Every round, the Bloodthirster advances towards the Devastator, and ends his turn behind a giant rock, which somehow hides his entire massive frame, providing a new set of cover (12) to all locations. Every round, the Devastator uses Hip Shooting to fire a single shot at the Bloodthirster, and moves away from him, to a new position of cover as well.
Thanks to the Imperial Fist solo mode ability, the Devastator ignores half the cover bonus the Bloodthirster enjoys, treating his cover as 6. Thanks to the Felling special quality, his lascannon shots ignore 6 points of Toughness bonus from the Bloodthirster, reducing it to 12. Firing a single shot qualifies it for the eye of vengeance, and since he is testing against 130 (70 + 30 (massive) + 10 (Red dot sight) + 10 (Signature Wargear) + 10 (Devastator ability Immovable Warrior)), and can re-roll atacks against the Bloodthirster should he somehow miss, he never misses during the course of this battle, and getting an average of 7 degrees of success, ignores an additional 7 points of armor. With a base pen of 10, that means the total damage is reduced by 14.
Each shot, having the proven (3) quality and automatically confirming Righteous Fury, deals an average of 6.4 damage per die, for a total of (6.4x5+10 (lascannon) + 2 (mighty shot) + 2 (master crafted)) 46 damage per hit. When hit, the Bloodthirster suffers d5 wounds (average 2.5) not reduced by Armor or Toughness, as a result of not having any other targets or weapons with greater than melee range, thus being unable to fulfill the conditions for avoiding damage from Warp Instability. As it's only a single shot, the Bloodthirster can attempt to dodge every time, and has a 40% chance to dodge (base 50 - 10 for the targeter), with no protection fields or other defensive countermeasures in play. This results in an average of (46 - 14 = 32 damage per hit, +2.5 (warp instability), x 60% success rate) 20.7 damage per round.
With 195 wounds, it takes 10 rounds of fire to bring the Bloodthirster down, which means the weapon must be reloaded once (taking one full round action to do so). The Bloodthirster, running every turn, closes 48 meters per turn. The Iron Fist, hip shooting, adds 14 meters to the distance between them each turn, excepting the turn he spends a full round action reloading. After 11 rounds of combat, the Bloodthirster has closed 388 meters of the distance between them, leaving 112 meters remaining.
Alternately, the Bloodthirster can fly each turn, moving 60 meters with his run action instead of 48, but losing the benefit of cover. Doing so results in him taking 24.3 damage per turn, requiring 9 turns of firing to slay, thus taking 10 rounds of combat, which means he ends having closed 474 meters of the range, ending the turn before he would have been able to charge (even if he went first, his last turn he has closed 488 meters using his run action, not quite there).
It should be noted that the Bloodthirster does have one method mechanically for an assured win in this scenario. As a flyer, he can move up to High Altitude as early as its second turn (long before it has suffered a significant amount of damage), and traverse the remaining distance entirely immune to attack, moving down to hovering altitude during its charge once it is directly over the devastator, and allowing it to engage in melee after having suffered a maximum of 3 hits (2 initially, 1 from overwatch). However, though I know the altitude rules are a carry over from tabletop, I reject them, as it means the Bloodthirster is somehow closing from beyond 1200 meters (extreme range for lascannons) to melee range with a single charge action (which would normally have a distance of 48m). Even accounting for speed from diving, that is exceedingly unrealistic. As a result, I am not taking that method (or those rules) into account in my simulations.