I'd like to reserve Offensive Gliscor and Defensive Jirachi.
Gliscor
Typing: Ground / Flying
Base Stats: 75 HP / 95 Atk / 125 Def / 45 SpA / 75 SpD / 95 Spe
Abilities: Hyper Cutter / Sand Veil / Poison Heal (Dream World: Released)
Despite being thought of as a primarily defensive threat, Gliscor's stats, movepool, and typing lend themselves to effective offensive sets as well. With its bulk and decent speed, it is able to easily switch into top threats such as Tyranitar and Lucario and threaten them with its STAB Earthquake. It can then use Swords Dance to boost its attack as they switch out, activating the Toxic Orb (and thus its Poison Heal ability) at the same time. Such a set up allows Gliscor to protect itself from status, gradually restore its health, and threaten the opposing team at the same time. Along with Swords Dance, Gliscor will typically use Earthquake as a powerful STAB attack while supplementing it with some combination of Stone Edge, Taunt, Ice Fang, and even Protect. An alternative is to run Fling on the set, allowing Gliscor to effectively use a full-powered Acrobatics attack alongside Earthquake and, in doing so, score super-effective hits on 8 of the 17 types with its STAB attacks alone. Without having a plan to check offensive Gliscor, it can become difficult to stop and will easily sweep a team with its coverage, power, and bulk.
Jirachi
Typing: Steel / Psychic
Base Stats: 100 HP / 100 Atk / 100 Def / 100 SpA / 100 SpD / 100 Spe
Abilities: Serene Grace
Thanks to its balanced HP and defensive stats, which are some of the bulkiest in the standard tier, Jirachi is highly adept at taking advantage of its excellent defensive typing to serve as a roadblock to an impending sweep, and it has the movepool to support this as well. Jirachi is often seen spreading paralysis to the opposing team, using either Thunder Wave or Body Slam, which has a 60% chance of paralysis thanks to Serene Grace. Being a normal-type attack, it gives Jirachi an exploitable niche in paralyzing ground-types, though it is unable to paralyze ghosts should it be chosen. Jirachi is also capable of setting up Reflect and Light Screen, and serves as a great check to dragon-types, particularly Latios, due to its typing. However, the main draw of using defensive Jirachi is Wish. Having so many resistances, great bulk, and being faster than a variety of offensive threats even without speed investment, the genie can easily use the attack to restore its own health or that of a teammate, and does so reliably throughout the match. As it often carries maximum EV investment in HP, defensive Jirachi finds itself restoring up to 202 HP on any recipient of its Wish, which can often revitalize a teammate worn down by hazards, Life Orb recoil, or an untimely misprediction. Thus, Jirachi is a defensive threat that, if left unchecked, will render damage to the rest of the team null and void. Be sure to pack Fire- or Ground-type attacks to deal with the star - it is notoriously difficult to 2HKO otherwise.