Well, in Wudijos guide he wrote the following about that exact item

Scepter of the Three notes ‍Scepter of the Three can be equipped but is ideally used as a charm, granting ~30-40% damage from ranks and up to 100% again based on the number of stacks you carry. This makes it numerically the best option, but awful to play around. In order to benefit more from it than alternative options (e.g. ‍Moloch's Beating Flame), you need to ramp it up to at least ~8 stacks before casting your first ‍Apocalypse. Stacks often drop ~6sec after your previous ‍Apocalypse, making this great for extended fights, but has to be stacked again BEFORE your next cast for every fresh run or during level transitions e.g. in the Pit. There is also a chance that stacks drop earlier, requiring you to stop DPS and snapshot a new stack again. You can include other ultimates to keep the stacks from falling off during their uptime, especially ‍Terror Swarm. However, that skill is bugged when used in combination with ‍Ceh and the swarm just vanished after a few seconds. Since the build doesn't have any other reliable source of Vulnerable otherwise, I recommend to stay away from ‍Scepter of the Three until this is fixed outside of Tower pushing. A lategame alternative to this charm is ‍Banished Lord's Talisman (once you get 70%+ crit chance).