Void Golem - Fremont

Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.

Immutable Form. The golem is immune to any spell or effect that would alter its form.

Legendary Resistance (2/day). If the golem fails a saving throw, it can choose to succeed instead.

Retribution. At the end of each round Fremont's Staff sends out a 500ft. pulse that does radiant damage equal to the direct damage the golem received this round to all creatures that dealt directly dealt damage to it. This also dispells any magical effect which spell level is lower than a tenth of the damage the golem has taken.

Reconstruction. The golem regenerates 30 hitpoints at the beginning of its turn. If it takes thunder damage, this trait doesn't function at the start of his next turn. 

Soul Bond. One creature of the golem's choice within 60ft. must succeed a DC19 Wisdom Saving Throw or become bonded with the golem. While bonded the golem has resistance to all damage. Also, each time the bonded creature takes damage, a the golem take the same amount of damage. 
A bonded creatures can't attack or cast harmful spells onto the golem or take damage from Retribution.
Bonded creatures can't move away further than 60 feet and can't teleport or enter other planes. A creature can use its action to repeat the Saving Throw breaking the bond on success.