As the title says, Body Slam does not hit a Minimize mon 100% of the time. Why is this important? Because, according to Bulbapedia, “Generation VI onward
If the target has used Minimize, Body Slam now deals double its regular damage and bypasses accuracy checks to always hit, unless the target is in the semi-invulnerable turn of a move such as Dig or Fly.”
I ran into a situation where Harmony’s Mega Miltank used body slam on a minimize Delta Muk and it missed.