Based on the above, and given that we know there's a Water/Fairy type in the mix, you can figure out that you need a dragon with a secondary type that is week to both fire and electric. But, that's impossible...
In other words, a mistake has been made somewhere. The only thing that PMJ actually hasn't confirmed is the abilities of the previous guess, and as such I have concluded that Marowak does not have Lightning Rod.
So in order to remove both the fire and electric resistance, we need a Dragon/Grass Pokemon with the ability Lightning Rod.
And finally, to deal with our ground immunity, we need a Flying/Bug type from the PU tier. Fortunately, there are only 7 to chose from.
PMJ, we think this is your team:
1: Alolan Marowak
2: Keldeo
3: Miltank
4: Azumarill
5: Mega Sceptile
6: Ninjask
In other words, a mistake has been made somewhere. The only thing that PMJ actually hasn't confirmed is the abilities of the previous guess, and as such I have concluded that Marowak does not have Lightning Rod.
So in order to remove both the fire and electric resistance, we need a Dragon/Grass Pokemon with the ability Lightning Rod.
And finally, to deal with our ground immunity, we need a Flying/Bug type from the PU tier. Fortunately, there are only 7 to chose from.
PMJ, we think this is your team:
1: Alolan Marowak
2: Keldeo
3: Miltank
4: Azumarill
5: Mega Sceptile
6: Ninjask