With access to the excellent BoltBeam combo, Thunder Wave, and an amazing Special Defense stat allowing it to tank most special attacks comfortably, Regice is quite a cool Pokemon to use in NU. It has the ability to reliably check Gorebyss, one of the most powerful special attackers in NU, and can easily spread paralysis around thanks to its STAB Ice attacks threatening Ground-types who may try to come in to block Thunder Wave. Pokemon who can break through Regice's defenses, such as Sawk and Charizard, are also threatened by Thunder Wave.
However, while it may have amazing special bulk and decent physical bulk, Regice's ability to tank various hits is offset by its horrendous Ice typing. Ice only grants Regice a resistance to itself, which is almost never useful. To make things worse, Ice also gives Regice a plethora of weaknesses to common attacking types, such as Rock and Fighting. As it is weak to Stealth Rock, vulnerable to all hazards, and lacks reliable recovery, Regice is fairly easy to wear down. Despite all this, if your team has issues with powerful special attackers and if you could use the paralysis support, Regice is not a bad choice for your team. You should note, however, that it's hard to cover all of Regice's weaknesses.
RestTalk is a generally disliked strategy in BW thanks to the new sleep mechanics; if Regice can't stay in for three turns at a time, it'll have to rely on the unreliable Sleep Talk to do any damage. The lack of Thunder Wave makes this set even easier to switch into. RestTalk Regice boasts a key advantage over other sets: survivability. Regice will be able to survive longer using this set, as it can Rest whenever necessary and still maintain the ability to check the threats it needs to, given a little luck. Thunderbolt and Ice Beam are used for optimal coverage.Team Options & Additional Comments >>>
Threats such as Gorebyss run rampant in NU, and this set aims to successfully check them while not giving other sweepers an opportunity to switch in. Regice's Special Attack isn't amazing, so it has to use Thunder Wave to threaten Pokemon that attempt to switch in on it. Ice Beam is Regice's STAB move of choice, but only really hits 4x weak targets, such as Torterra and Altaria, hard. Thunderbolt complements Ice Beam well, allowing Regice to hit the likes of Gorebyss and Samurott. Rest is an unreliable move thanks to the new sleep mechanics, but Regice needs some kind of recovery as it is easily weakened, which is where Rest + Chesto Berry comes in. It's not like Regice actually misses Leftovers, as it's usually only out for a few turns, nor does it really miss whatever else it can use in the last slot, as it doesn't have many options.Team Options & Additional Comments >>>
It might be surprising that a defensive behemoth like Regice has the potential to be one of the most devastating offensive Pokemon in the tier, but it has all the right tools to be an amazing late-game cleaner. Rock Polish is what makes this set truly frightening, allowing a boosted Regice to outrun everything up to and including Jolly Swellow while also being extremely easy to set up due to Regice's great bulk. Ice Beam is Regice's most reliable STAB attack, ripping Grass-types, such as Roselia, as well as Flying-types, such as Rotom-S, to shreds. Thunderbolt offers great coverage along with Ice Beam, forming the famous BoltBeam combination, renowned for being very difficult to resist. The primary reason to use Thunderbolt is to stand up to Water-types, in particular Samurott and Carracosta, which can threaten Regice with Waterfall and Stone Edge, respectively. Focus Blast allows Regice to hit certain Pokemon that resist BoltBeam, such as Rotom-F and Piloswine, super effectively. Focus Blast is also Regice's best option against opposing Regice, as well as bulky Normal-types, such as Miltank and Lickilicky, that can shrug off an Ice Beam with ease.Team Options & Additional Comments >>>
Charge Beam is an interesting setup option that gives Regice a way to improve its decent Special Attack stat. However, note that Regice is very slow and Charge Beam eats up a useful moveslot, in which Regice could otherwise run Thunder Wave to cripple sweepers or Rest for semi-reliable recovery. Curse is a more defensive setup option that patches up Regice's low Defense to an extent, but a physically based Regice would have to use the weak Ice Punch and ThunderPunch off of base 50 Attack.
Regice can actually use set-up opponents to its advantage by using Psych Up to obtain their boosts and then Frost Breath to negate their Special Defense boosts. It's a pretty gimmicky option, however, as Calm Mind users would usually switch out of Regice at first sight, and it leaves Regice as susceptible as ever to physical attacks. Finally, Toxic is a decent option on any defensive Pokemon, but Regice should be spending its time spreading paralysis as it threatens Ground-types well; paralysis also helps Regice get past checks such as Sawk and Braviary.
Checks and Counters
As with any Stealth Rock-weak Pokemon, having it up cripples Regice. Regice struggles with walling threats such as Gorebyss after it takes Stealth Rock damage; therefore, if you can manage to keep Stealth Rock up throughout the match, Regice will be a lot less threatening. Camerupt and Piloswine can set up Stealth Rock well and don't care about anything Regice throws at them other than the rare Toxic. Gurdurr and Throh can also switch into Regice with ease, and even enjoy switching into Thunder Wave thanks to Guts. More examples of Pokemon that can switch into Regice without being crippled or taking much damage include Lickilicky, Miltank, and Audino, who can also remove status with Heal Bell.
You might have noticed that many of Regice's checks are defensive; however, offense doesn't struggle that much against Regice either. While offensive teams tend to lack good switch-ins to Regice, as long as they can avoid switching into Thunder Wave, Regice shouldn't be too threatening to them. Pokemon such as Sawk can swiftly KO Regice before it can deal any damage to it, and Charizard and Braviary can also put a dent into Regice, especially if Stealth Rock is up. Regice generally isn't that hard to beat; just don't keep your special attacker in on it unless it can manage to muscle through Regice, or if you can afford to sacrifice it.
Ice Body would have been an effective ability for Regice back when hail was in NU; unfortunately, with the Snow Warning ban, Ice Body is now useless.