Pre-balance: 100 LUK = immunity to stone curse
Post-balance: 100 MDEF = immunity to stone curse
Sienna calculates its success rate 2 times.
1. Calculates skill's base success chance. (45 + 5*Skill level)%
2. Calculates target(s)'s immunity.
If calculation #1 returns fail, you will see your warlock casting Sienna Execrate but no animation on the target.
If calculation #1 returns success, you will see skill animation on the target (animation looks like a stapo) and if the target is immune to stone curse status, nothing will happen.