Ultimatum is an active ability in Sonny 2.
Heals you for 100% of your Health, and decreases all damage and healing taken by 95%. But you lose 10% of your Health each turn.
Heals the target for 100% of its health, and applies the buff "Ultimatum" for 20 turns. The buff actually damages for 5% HP each turn.
Ultimatum: This unit receives 95% less damage and healing, but suffers 10% of its Health as damage each turn. Time is running out.
What Ultimatum actually does is heal the target for 100% of its health, and applies the buff Ultimatum, which lasts for 20 turns. This buff first reduces damage and healing received by 95% then damages for 100% of its health, which effectively does 5% damage. Therefore, buffs that reduce damage by 5% or more will effectively make the target immune to damage. This is most notable with Roald's Greater Purpose, which essentially would make the player invulnerable. Another tactic is to purposely make yourself a target by lowering your max health below your teammates, and draw fire while still outputting maximum damage - useful in countering Yosuke and the troublesome dogs in Zone 5.
Interactions with other skills Edit
Ultimatum and Overdrive's effects apply to each other, meaning that Overdrive only does 0.0475% of the target's maximum health, and Ultimatum effectively does 10% of the target's maximum health.
As noted above, damage is being reduced by 95% damage before it is applied. Thus, there are 3 ways to counter Ultimatum's effects: using abilities that reduce damage by a flat rate, percentage amounts will increase suitability rates, or healing more than damage received.
Greater Purpose reduces damage taken by 40%, resulting in a 135% damage reduction; damage received will either do 1 or no damage at all.
Shields like Free Will will soak up the remaining damage that you receive; proper usage will ensure survival.
There are various ways to heal off damage: General heals will work; Retrograde during the last turn of Ultimatum, then Nightmare. Using Nightmare during the last turn of Ultimatum is effective, as the damage is reduced but the healing isn't.
Generally however, this ability is designed as a last resort. You can simply be relentless against your opponents for the next 20 turns in hopes of defeating them before you die yourself.