Golbat

Everything about Golbat just screams defensive Pokemon. It has a great defensive typing, being 4x resistant to the common Grass-, Fighting-, and Bug-type moves in the RU tier, as well as having immunities to both Ground-type moves and Toxic. Eviolite boosts Golbat's already decent defenses to great levels, and when in conjunction with Roost, Golbat becomes nigh impossible to kill. A good Speed stat allows Golbat to outspeed most of the common walls in the tier, Taunting them before they can retaliate. However, Golbat suffers from a crippling weakness to the common Psychic-, Electric-, Ice-, and Rock-type moves, as well as Stealth Rock. However, this won't stop Golbat, as it's still one of the best checks to Fighting-, Grass-, and Bug-types in the tier, and makes for a solid defensive threat.