Chaos Zero Nightmare: Rossweisse Viadeus 9/9 OTK Guide

To defeat Viadeus at difficulty 9/9 in a single turn using Rossweisse in Chaos Zero Nightmare, you must frontload all Action Point (AP) generation, apply defense shred before striking, and unload her burst cards in ascending order of damage. Bypassing the boss's multi-phase counter-mechanics requires spending every point of AP on Turn 1 strictly for damage amplification and execution.

Viadeus 9/9 OTK Requirements

Viadeus 9/9 features aggressive health scaling and counterattacks that punish prolonged fights. Executing a One-Turn Kill (OTK) eliminates these mechanics entirely, provided your team meets three criteria on the opening turn:

• Instant Turn-One Value: Every buff, debuff, and relic effect must trigger immediately at combat start. Do not run ramping abilities that require multiple turns to stack.
• AP and Draw Concentration: All bonus AP and card cycling must feed Rossweisse's damaging cards. Spending AP on shielding or healing guarantees the attempt will fall short.
• Pre-Damage Defense Shred: Viadeus must have active defense-reduction or vulnerability debuffs applied before Rossweisse plays her first damaging skill.

Recommended Team Roles

Rossweisse serves as the sole damage carry. The remaining three team slots exist exclusively to set up her damage window.

Step-by-Step Turn-One Card Rotation

Follow this exact sequence to ensure all multipliers are active when Rossweisse's highest-cost attacks resolve:

1. Generate AP and Draw Cards: Play zero-cost and AP-positive support cards first. Resolve all card-draw effects before spending AP on attacks to confirm your combo pieces are in hand.
2. Apply Vulnerability to Viadeus: Cast your debuffer’s defense-shredding abilities on Viadeus. Never hit the boss with Rossweisse while base defenses remain intact.
3. Trigger Rossweisse’s Setup Skills: Cast Rossweisse’s self-buffs to guarantee critical strikes or prime her next skill multipliers.
4. Initiate the Burst Chain: Play Rossweisse’s intermediate attack cards. Prioritize cards that refund AP, draw follow-up attacks, or build damage stacks upon hit.
5. Cast the Finisher: Spend your remaining AP on Rossweisse’s highest-multiplier burst card to deplete the rest of Viadeus's health bar.

Rossweisse Stat Priorities and Deck Tuning

Because the strategy relies entirely on Turn 1 execution, stat consistency is mandatory:

• Critical Rate (100% Effective): Calculate your base stat combined with party buffs and passive skills. Missing a single critical strike during the burst chain will break the OTK threshold.
• Critical Damage: Once Critical Rate reaches the effective cap, invest heavily in Critical Damage to scale Rossweisse’s multipliers.
• Attack (Flat and Percentage): Maintain a high baseline Attack value so percentage buffs deliver full value.
• Speed Tuning: Ensure your buffer and debuffer have higher base Speed than Rossweisse so their cards enter your hand and resolve before her attacks.
• Deck Culling: Remove unnecessary defensive and utility cards before the run to reduce draw variance on Turn 1. Prioritize card enhancements that refund AP or lower skill costs.

Common Failure Points

• Miscounting Action Points: Playing an intermediate attack without tracking remaining energy can leave you short of the AP needed for your finisher. Calculate your net AP gains from support skills before committing to attacks.
• Debuff Resistance: If Viadeus resists an opening defense shred due to low debuffer hit stats, abort the burst attempt, as Rossweisse cannot overcome the boss's raw baseline defenses alone.
• Opening Hand Bloat: If drawing utility cards prevents pulling Rossweisse's core sequence on Turn 1, reduce overall deck size to improve opening hand consistency.