If Zhan had visible eyes instead of just a smooth silver oval of a head, those nonexistent eyes would have widened. For a slime, who does not see through reflections of light but rather through changes in the atmosphere and sensing of energy, Alexander's form had suddenly become blinding. No sooner had the medallion from Ares been activated than did Zhan halt his attack and move to retract his arms, whilst Alexander stepped back to avoid the attack that Zhan had hastily canceled. 

The Metal Slime, with Alexander's abandoned shield in possession, quickly darted back, putting some distance between himself and the Ares Guild member. "...that isn't your own power. Those damnable overseers of yours..." He seethed, continuing to edge backwards along the room, evidently unwilling to continue fighting Alexander. While Zhan was confident in his survivability, the class of being that Alexander had just stepped into the bounds of wasn't something he wanted to take chances with; the Floor Guardian had little doubt that this wasn't some sort of unsealed state, and was more likely a temporary increase in power. This human was stronger than him for the time being, yes, but it was not permanent, and moreover the human had no way of locating his core, even if his slime could now be damaged. In that sense, Zhan simply had to switch gears from blitz to attrition; if the human decided to retreat, then so be it; when he returned he would be weaker than he was currently.