An interesting card choice that i enjoy. While i dont have the cards to run this, i feel like this pokemon is actually pretty decent in a funny way.
Milling is usually not a very good strategy to build a deck around. Granted it has worked with the Durant Milling deck with some moderate success. You will probably never win any real tournaments with this deck but it can be quite annoying.
Aggron has a decent amount of HP, as well as its previous evolution Larion with 90 HP. It's attack is pretty darn terrible though. For MMC it does 90 damage that if you flip 2 tails, it does nothing. Though you dont use this card for it's attack.
Toppling Wind discards 3 cards from the opponents deck when it evolves. Imo its pretty decent in terms of evolution abilities. To bad its on a 2nd step. The only way to really work this card involves devolution spray and like a 4-4-4 line of aggron with some sort of pokemon to take hits or another pokemon that can effectively mill the opponent as well.
The art itself i find to be decent. Its not terrible, but its also nothing special.
Overall i say this card is sort of meh. Even considering the fact that i enjoy using weird decks.