Anything mobile that can readily deal damage to a construct works well.
A
golembane scarab or a
Greater Weapon Crystal of Demolition are relatively inexpensive items that would help a physical attacker.
Perhaps a kelvezu with the ability to cast
Golem Strike by means of class levels or the UMD skill, to enable their sneak attack damage to harm the construct, might prove troublesome.
Disintigration effects are worth using.
Assuming Xukhezur doesn't have a
Ray Deflection effect in place,
Ray of Deanimation can be pretty effective, especially for sneak attacking with the above mentioned golem strike.
Orb spells using the right energy types can also be effective, especially if paired with the searing fire or peircing cold feats.
Assay Spell Resistance and
Crumble are worth looking at as well.
Although Xukhezur is an artificer and can repair his construct... once that construct is destroyed, there is no bringing it back, and any back up construct Xukhezur employs, will have next to none protomorphic modifications made to it, since it takes at least 1 hour to use that infusion, meaning it will be slower and weaker until Xukhezur can buy the time to use it.
If you delve into pathfinder for inspiration, you have spells like
Apparent Master and
Control Construct that would prove effective, especially if you command a
mecha to release or eject its occupant.
I also personally think that any creature with the appropriate knowledge ranks, should be able to take and use the
Construct Lock feat.