This is Regigigas; he needs no introduction, as with stats like his, everyone knows that he should be able to do some serious damage. Unfortunately, the biggest letdown with Regigigas is that in order for him to 'do serious damage', he has to survive five turns in battle before his crippling ability, Slow Start, wears off. During those five turns, the opponent almost always either massacres Regigigas or does whatever he or she pleases and phazes him at the last possible moment.
Regigigas isn't all bad news, though, and can actually do something useful in the UU tier, where his raw defensive stats make his survival possible. Base 110 defenses across the board are tough to break, and the general lack of phazers helps Regigigas even more. Once Regigigas has stalled those five turns, he can proceed to crush skulls with his base 160 Attack stat and base 100 Speed stat. While he may not be the prodigal son of legendary Pokemon, Regigigas can certainly hold his own in a tier that isn't used to dealing with Pokemon of his stature.
The first order of business for any offensively minded Regigigas is to stall out the Slow Start turns so Regigigas can grind bones to make his bread. Because Regigigas lacks obvious means to do this, such as Rest and Protect, more creative methods are employed.
Thunder Wave slows opposing Pokemon down so that even Regigigas can outspeed them and then either repeatedly Substitute or employ Confuse Ray to complete the parafusion combo. Both strategies work effectively in different situations for stalling the Slow Start turns, but Regigigas's Substitutes are notoriously difficult to break without super effective or very powerful STAB attacks, generally making Substitute the way to go. In the last slot, Earthquake and Fire Punch are both useful. Earthquake leaves Regigigas helpless against the commonly seen Ground-immune Ghost-types of UU, Mismagius and Rotom, whereas Fire Punch is much weaker and will make it difficult to break through Rhyperior, Omastar, and even Kabutops.Team Options & Additional Comments >>>
Regigigas actually has one of the best sets of combined defensive stats of any Pokemon in the tier, beating out even Uxie and Milotic. Couple this defensive prowess with the potential to do serious damage after Slow Start has worn off and Regigigas can pose a serious threat to any team without super effective Fighting-type attacks to fight back with.
Return and one of Earthquake or Fire Punch are Regigigas's attacking options. With Earthquake, Ghost-type Pokemon are an issue, and with Fire Punch, Rock-type Pokemon are a problem. In the third slot, either Thunder Wave or Toxic is selected to cripple opposing Pokemon. Lastly, Knock Off is a really irritating move to hit anything with, as virtually every Pokemon in the game relies on their item to some extent. Choice Band Rhyperior will hate losing that power, while Hitmontop and Hitmonlee will be loath to lose Leftovers and Choice Scarf, respectively.Team Options & Additional Comments >>>
Regigigas doesn't have a shallow movepool by any means, but almost all of his worthwhile options are rendered useless by Slow Start. Rock Polish would be great if he wasn't at half Speed and Attack for 5 turns. A set consisting of Focus Punch and Substitute might sound great on paper, but it's pretty terrible when you factor in Slow Start's effect on Regigigas's Attack and the lack of STAB. Outside of that, Regigigas has a decent special movepool in Thunderbolt, Focus Blast, and Earth Power, but lacks both the Special Attack and the Speed to utilize it effectively.
Checks and Counters
Regigigas's best responses are Fighting-type Pokemon. No matter which attacking moves Regigigas runs, Fighting-type Pokemon will trouble him. Hitmontop tops this list—no pun intended—with Intimidate to catch Regigigas before he can Substitute and STAB Close Combat to eliminate him. After Hitmontop, Guts Hariyama is a superb response because of Guts turning status used against it into a deadly weapon. Lastly, Hitmonlee is also an excellent choice because of his immunity to Thunder Wave and immense power. Bulky Ghost-type Pokemon fare well against Regigigas even if he carries Fire Punch; they are immune to Regigigas's only STAB and will do quite a bit of damage if they pack Hidden Power Fighting.
One of the worst things you can do is try to stall Regigigas out with Pokemon like Steelix or Chansey. If Slow Start ever wears off, your Pokemon will be in for a world of hurt. The only time you should attempt to stall Regigigas out is if you have Toxic Spikes in play. If Regigigas gets poisoned, he is pretty much dead in the water, as he then no longer has even the slimmest chance to stall out Slow Start. Phazing is also one of the best ways to deal with Regigigas; Perish Song, Whirlwind, and Roar will all force Regigigas out prematurely, killing any chance he has of threatening your team.