1.Stats: Should Hippowdon get a stat boost, Evolution, Mega Evolution or nothing?
Hippowdon already has 195 BST gap, which is more than enough, but it can get one more 10 stat buff to maximize its potential stat. Because it evolves very late, an evolution can only be achieved if it were a stat distribution change evolution, like Scizor or Porygon-Z.
However, the only likely solution(if there is any needed) to Hippowdon is a Mega, which will be largely useful all around.
2.Should Hippowdon get more abilities?
Yes. Hippowdon has room for one more Ability, which will likely be used for a new Ability.
For existing ones however, the following might be fitting,
- Arena Trap
- Sand Rush
- Sand Veil
- Strong Jaw
3. Should Hippowdon get more moves?
Yes, as Hippowdon's moveset is largely limited to Ground-type moves. Some obvious moves would be Payback, Zen Headbutt, Counter and Spikes.
4.What additional typing Hippowdon can have?
Dark and normal are the most obvious ones, Rock, Steel and Fighting are the lesser obvious ones.