Steelix

Thanks to its unique typing, Steelix manages to check certain Pokemon other Ground-types would struggle to deal with, such as Meloetta and Magneton, and it has two handy immunities to Poison and Electric, meaning that it is immune to status-inducing moves in Toxic and Thunder Wave, with the former giving it another notable advantage over other Ground-type Pokemon such as Rhyperior by preventing it from getting worn down as easily. Steelix's massive Defense stat lets it focus on investing mainly in Special Defense to make the most efficient use of its EVs and improve its bulk. Steelix is also much more immediately threatening than other defensive Steel-types like Bronzong and Registeel, make Steelix a nice choice for some teams.

However, compared to other Ground-types, it is much more passive and really struggles to beat opposing Ground-types, since most of them can beat it one-on-one pretty easily. An unfortunate neutrality to Ice-type attacks means it won't be dealing with Pokemon like Abomasnow and Mega Glalie anytime soon unlike its Steel-type comrades. Furthermore, unlike Rhyperior, Flygon, and Seismitoad, Steelix lacks the offensive presence to threaten Grass-types, and this is another thing to be aware of when using this Pokemon.