I believe I found an error with the calculator, either that or I'm doing something wrong.
Here is what the calc with the battle tree sets gives me:
0 SpA Slowbro-Mega Scald vs. 252 HP / 0- SpD Magmortar: 66-78 (36.2 - 42.8%) -- guaranteed 3HKO
0 SpA Slowbro-Mega Psychic vs. 252 HP / 0- SpD...