Here's an idea:
Instead of that bomy health meter, you could create an entirely new meter exclusively for Zulites. I think the meter could include how much "energy" it has (determines the power/velocity of the roll), and an indicator that tells you how close the Zulite's rocky skin is to becoming a pile of rubble
. Maybe Zulites, unlike the other races, wouldn't measure each hit by a set amount (i.e. .5 hearts, 1 heart, etc), but instead they'd measure the damage by its effectiveness. Like if a player hits a Zulite with a blunt sword, they'll get very little damage that can be replenished automatically. But if they're hit with an oil drill, it spells out sudden death
So basically, if your weapons are weak, you'd have to keep hitting the Zulite so it doesn't have a chance to replenish.