They're in the game data so it's fair game to talk about them. Credit for the discovery goes to Deathmax; these were added shortly after Adriesta was fixed.

This new line of Guild Spheres may be added to the game in the near future (or not, Gimu might change their mind), so for those of you just finishing your current Guild Spheres, read on and decide if you want to save your guild tokens for the new one:

Jeu'vrr's Warcry
Sphere Type: ATK Boosting
Effects: 250% BB ATK, 5 BC/turn, Add Effect to BB/SBB: Inflict DoT on All Enemies for 3 turns ( 1000% DoT ATK%, 100 DoT Flat ATK)

The sphere recipe is similar to the previous guild spheres; 14 and 9 guild materials for the first upgrade, and 17/12/10 guild materials for the second upgrade (plus some honor mats). The guild materials appear to be entirely new, so you can't get a head start by buying the currently available materials.

The new materials are:

• Shambler Cuttings (21 total needed for Warcry)
• Phrun Stingers (31 total needed for Warcry)
• Burbur Branch (10 total needed for Warcry)
• Centipede Fang

Centipede Fangs are not used for this sphere, suggesting that it has a pair sphere made with Centipede Fangs that may be released at the same time (Probably called Dehn's something, I guess). However, that sphere is not in the game data yet.

As for the weaker versions of the sphere, the first form "Jeu'vrr's Breath" just gives 150% BB ATK and 3 BC/turn, and the second form "Jeu'vrr's Oration" gives 200% BB ATK, 5 BC/turn and a 600% DoT.

Now, for the usage of this sphere... it seems designed with crit-resistant content in mind. The BB ATK is simple enough, but the DoT is mildly unusual because I normally explain DoTs relevant to the unit that has them. In this case, however, you'll need to know the relevant mechanic:

DoT Damage = ([(Base ATK Imps DoT Flat ATK) * (100% DoT ATK%)] - Enemy Buffed DEF/3) * Elemental Multiplier * RNG

The elemental multiplier is just the base /-50% damage for matching elements against their weak/resistant element respectively. EWD is not considered for DoT damage calculations. Note that DoT ignores elemental addition buffs on your unit; the DoT itself just inherits the unit's base element for future damage calculations, so a Fire unit's DoT only has the fire element, even if that unit had a water buff, and so on.

The RNG range is the same as regular attacks, rolling roughly 90-100% of the expected damage. This means you can expect the DoT to deal somewhere along the lines of 10-11x the unit's base ATK, with a little extra from the 100 bonus flat ATK, and a little less due to enemy DEF.

No other effects come into play; DoT goes through all mitigation sources (a potential niche in some content, by the way) and is unaffected by buffs other than DEF buffs/debuffs on the target.

As it only considers the base ATK and element of the unit applying the DoT, you most likely want to put it on a unit with high base ATK, probably Light/Dark element so it can't be resisted, and preferably one that also benefits significantly from added BB ATK. A good example unit would be Lauda, who would hit for nearly 50k with this DoT as Lord and get double the benefit from the BB ATK. Note however that if you can perfect spark him you may still get better squad damage by giving him a decent spark sphere.

The DoT from this sphere is added to the unit's BB/SBB via the same mechanic as SP enhancements. As a result, it won't stack with any unit's native DoT effect. It is, however, larger than any non-UBB DoT. If it clashes with a DoT the unit can already apply, it's very likely that the unit's own DoT will take precedence, so keep that in mind when deciding who to slot it to.

Note that this sphere is in the pre-release state, meaning its effects may be subject to change before release. However, there is still an unknown guild sphere likely to be released alongside it, so even if you don't want this BB ATK/DoT sphere, a new one may be coming which could still be worth saving those guild tokens for.