TL;DR at bottom

For this I am not including resistences or Immunities but I am including successful saves. So as the above question implies is that I got some sort of method. Thether Essense makes a creature take as much damage as the one it is chained to. Cause 10 damage to one & the other takes 10 damage. If you take Tempest Cleric twice you get the channel divinity which allows you to maximise damage output for thunder or lightning damage. Transmute Spell or Order of Scribes MS to change it to thunder/lightning then channel divinity to get a minimum of 60 Thunder damage on a succesful save plus 20d6 bludgeoning (min 10) now add the TE to double that for a possible minimum 140 minimum damage.

Besides this, I wouldn't know how to get that minimum higher. Open to hearing from people.

TL;DR (60 10) x 2 = 140