I've been thinking about this for awhile, but shura feels like it scales better to a bigger population.
While the gimmick is cool, I feel like this server has outgrown it. It's causing more problems and doesn't really add anything interesting to the current situation. They're really buggy still, they cause too many issues because there aren't enough people, and people are actively avoiding PVP on shura map days.
To and try to cultivate a better pvp environment without any hurt feelings, I think this would be the best course of action. One shura is enough to wipe all current players on the map as is, and it's hard enough getting balanced pvp as it is. Removing shura from the map or reducing the move speed, damage, and/or range is probably the best course of action.
However, I think the devil manta rays are ok. They're NPCS and not players, and have mechanics in place from them causing too many issues.
Let me know what you guys think!