>>29770870>>29770870Well there really aren't a lot of single-type mons defensive enough to round out the trio and the only things that resist Ground together are Bug and Grass and I think we all know how well that would go.
I vote Cradily.
>Hit neutral by Toxapex's Ground weakness and Ferrothorn's Fire weakness>Toxapex resists its Bug and Steel weaknesses (which will probably be contact moves, so Baneful Bunker)>Ferrothorn takes neutral damage from its Ice and Flying weaknesses (which will probably be physical, so Iron Barbs)>Cradily can set up Stealth Rock to cover 3/4 of its weaknesses and weaken other threats for Ferrothorn/Toxapex 