Mormons believe that Jesus Christ and the Holy Spirit aren’t distinct beings, but entirely separate - they are not Trinitarians in the least. However being tritheists are the least of the concerns here.
Mormons believe that “Heavenly Father” (aka “Elohim”) was once a normal human, who had a god father and goddess mother. Elohim then ascended to godhood, becoming who they refer to as “Heavenly Father”.
They believe that if you follow specific ordinances, you too can become a god or goddess. Upon becoming a god (with the possibility of having multipel goddess wives), you too can rule over your own universe, have a plethora of spirit children. Those spirit children then begin to gain physical bodies themselves, and begin their journey to godhood. Which is why this moves beyond tritheism and into outright paganism.
If you’re wondering where the starting point for this progression is, there’s isn’t one. Mormons believe in infinite progression, not an unmoved mover or uncaused cause. Elohim does not exist beyond time. When approached about Aristotle or Aquinas, thus far no Mormon has been able to present an answer to me or my wife.
To quote my wife; “my goal for eternal life is to worship, not to be worshiped”. Which is the opposite of Mormonism; the end goal is specifically designed for men to become gods, and to be worshiped themselves.
To that end, I would never ask for a Mormon blessing. When Mormons ask my wife and I if they could lead us in prayer, my wife and I decline, as their god is not our God. The god they worship and pray to is not infinite, not the Creator, not the unmoved mover. Their god was once a man, their god is a finite creature. Our God is infinite, He is Lord of all. He exists beyond the very fabric of time. There is no comparison between them. So instead we offer to lead the prayer, in which I will typically end by saying that we ask Christ to reveal His true nature to all, along with finishing with the sign of the Cross.