Everybody loves Ice Prison Necromancer, Cocytus. Granblue's currently only unit with Limit Break, Cocytus can revive any Granblue you want as soon as you ride him and pay CB 2. This is not that unit. Witch Doctor of the Abyss, Negromarl was Cocytus before Cocytus existed.
Like Cocytus after him, Negromarl can revive any Granblue in your drop zone at a cost of CB 2. Unlike Cocytus after him, Negromarl doesn't have a superior ride chain or the +5k limit break. He also doesn't even have 10,000 power. Negromarl is 8k in power and makes up for his physical weakness by being able to use his revive skill whether he's ridden or called.
Strategies and game play:
The most important thing for Negromarl is to not use too many of Negromarl. Even if he can use his skill from the vanguard circle, it's still a bad idea to linger with an 8k vanguard. Two or three Negromarl should be sufficient. Negromarl has no usefulness beyond its revive skill, so after that has been used it can be replaced by self-reviving units. Remember that self-revivers units usually have a lower cost than Negromarl, so they shouldn't be revived. Also of note is that Negromarl doesn't specify that it has to revive a Granblue. Technically it could revive Dragonic Overlord, then use Overlord's counterblast from the RG to demolish a front row. This is not recommended, since Negromarl only works if you control a Granblue vanguard, and getting a Dragonic Overlord to the drop zone would become difficult since sentinels and Chappie won't be able to mill him off. That being said, what should Negromarl target?
Combos with other cards:
Focusing on Granblue targets, Dancing Cutlass could be revived to use his skill, then replaced by the skill of a self-revive unit. An intercept would also be a good revive target, though Skeleton Swordsman (the 10k intercept) and Stormride Ghost Ship (Genocide Jack for Granblue) would work the best, Swordsman for his extra shield and Ghost Ship for its instant release restraint. Dragon Undead, Skull Dragon would be a decent revive target, as (unlike other self-revivers) it requires a Grade Two or higher sacrifice and is sent back to the drop zone at the end of the turn it attacked. A second Negromarl would be a suitable choice, enabling a second revive at the cost of a total of four CB. Use Pietro in a deck designed to use multiple Negromarl in the same turn. Another trick is to use Death Seeker Thanatos's skill to revive Negromarl, then use Negromarl's skill to revive a strong booster like Romario. This will eat up CBs, so again Pietro is recommended if the goal is to string together revive combos. Alternatively, Negromarl can be used to revive Death Seeker if you need to start off that combo.
Ways to counteract it:
Negromarl is physically weak and can't intercept or otherwise be used to guard (except as sentinel fodder). Hit Negromarl hard enough and it'll shatter. Meanwhile, if Negromarl happens to be the vanguard at the time, we suggest laughing at the other side's misfortune. Then you can hit him hard enough to make him shatter. Joking aside, it's incredibly easy to hit an 8k vanguard hard enough to force 15k guard.
Bring back any card that exists, so long as your vanguard is Granblue.
Bringing back cards outside of the clan is difficult for a deck relying on choose-your-own-mill cards like Chappie and Captain Nightkid. Negromarl is a low-power unit that can be taken out by nearly anything. Trying complicated revive combos requires a lot of setup and CBs.
Negromarl is a RR from the second booster pack. That's the only variation they have of him, although some consider Cocytus a "variation".
Artwork and aesthetics:
From the lore, Negromarl is also a Necromancer (hmmm, there may be some connection between him and Cocytus after all), though his methods seem to be more reminiscent of a puppet master than a true necromancer. Even the artwork seems to suggest this, with the blue blurry whatever-it-is in his left hand looking vaguely like strings.
Negromarl can revive anything (7) at moderately high CB cost (-1) and is the weakest Grade Three in terms of printed power in the game (-2), though as a Granblue it can be sacrificed to bring back something better once its skill is used (+1). Negromarl is worth 5 out of 10.