On a single glance, it would seem that the Players' strategy against the Sakasugi the Dead Red Dragon was working steadily.
Being a dragon, the creature itself embodied Rule Resistance.
Even so, that resistance faded as time passed, and Sakasugi couldn't retain the last fraction of resistance when it was revived as a zombie. Though its base stats were as high as it had been before and it could instakill any non-tank Players below Level 40 with a slap, it was not permanently Immune—the one status that bothered Players the most.
Moreover, having no Rule Resistance meant that the Players could deal -1 HP damage to Sakasugi even if they couldn't pierce its defenses, since they would be backed by Rule of Skill whenever they cast their skills.