A powerful EGO that can hit many skill slots in the battlefield. At lower uptie levels, its main draw is being able to hit as many as 5 opponents all at once, dealing significant Pierce damage and inflicting some Rupture on them. The Rupture itself doesn't do much, as it only inflicts Potency and not Count.
At uptie III and above, the EGO gets an additional buff: Inflicting 2 Gluttony Fragility on hit. This can be a boon for certain other skills or EGOs that are Gluttony in nature, such as Gregor's Legerdemain EGO or Tingtang Hong Lu's Mutilate. The EGO then evolves into both a hard-hitting AoE hitter and a Gluttony debuffer as well. It helps that its skill power is decent overall, going from 19 base power (22 at uptie III) to 26 total power (29 at uptie III) if its single coin flips heads.
The skill itself can also inflict Bleed if it manages to hit heads, but this should be treated more as a bonus, as neither the EGO passive nor any of Outis's current IDs can support Bleed and make it viable with this EGO in mind, especially considering how expensive it is to even use.
Quite a few but significant differences here. While the overall debuffs that Ebony Stem inflicts on enemies is the same, the amount inflicted is more than the Awakening version.
For instance, while Awakening only inflicts 2 Rupture and Bleed, Corrosion instead inflicts 5 of each. Not a significant amount still, but the Rupture potency can pull the damage of Rupture up, especially if the Passive from this EGO is active and the enemy has decent Rupture stacks on them..
The amount of Gluttony Fragility also gets an upgrade here, as the EGO now inflicts 3 instead of 2 like in the Awakening version.
Its overall base power gets a pretty big boost too. The skill starts at 26 (29 at uptie III) base power, essentially the maximum power of Awakening Ebony Stem, and can reach a maximum of 33 (36 at uptie III) power. This means that while the SP can be costly to activate corrosion, you have a much higher chance of winning a clash with Corrosion Ebony Stem than you would with Awakening, as its minimum roll is Awakening's maximum roll.
The passive itself is pretty neat. Outis gets 1 Pierce DMG Up for the rest of the battle, boosting the damage prowess of Ebony Stem if she decides to use it again, or any other Pierce skills and EGOs she might have.
She also has the potential to inflict Bind and Rupture when hitting enemies with a coin that flips heads, though this may be a bit difficult initially due to Ebony Stem using up a good amount of Outis's SP in the previous turn. But otherwise, the passive helps control the speed of enemies while also buffing her Rupture prowess, making it easier to stack Rupture with Identities like Seven Outis.
Ebony Stem is a solid Identity that sees a lot of use even when not uptied yet. Being one of the few EGOs out there that utilize AoE targeting from the getgo means that fights with multiple enemies or Abnormalities that have multiple body parts can be made much easier with the usage of Ebony Stem. The fact that it has 5 targeting slots is pretty big already. At uptie IV, it becomes 7 slots, but uptying the EGO to IV just for the slight increase in targeting slots may not really be worth it unless you have resources to spare, since it's quite expensive.
Higher uptie levels make Ebony Stem much more versatile, as not only can it target multiple enemies, it can now inflict even more debuffs and status effects, such as Rupture, Bleed, and Gluttony Fragility, turning the EGO into a hybrid of sorts in dealing damage and inflicting status effects for your allies to take advantage of in battle.
At minimum, you'll definitely want to uptie Ebony Stem to III for the additional status effect (Gluttony Fragility), but again, as mentioned earlier, Ebony Stem works perfectly fine as a standard AoE EGO skill even before uptie III due to how powerful it is.
It's quite expensive to even use, needing a mix of 2 Lust , 3 Gluttony, 1 Gloom, and 4 Pride EGO resources to even activate, but it's more than worth it for an EGO as useful and versatile as this one.