Hail is the hardest to use of the four major weather conditions, and with good reason- the only pokemon who benefit from it are Ice types, and not only is Ice a small type-listing, it’s not a very good type for your pokemon to be.  Hail is more like Sandstorm than the other weather abilities- but with less support and more restrictions, it’s simply not as good.  It isn’t terrible, but it’s not as good.

Hail is created by the move Hail for five turns, and can also be generated by the Snow Warning ability on Abomasnow.  As with the other weathers, it has an associated rock- the Icy Rock.  Since there are no obvious item choices for most pokemon that you would want Hail on, it is not as difficult to choose whether or not to give a pokemon the rock.

During a hailstorm, the only truly static effect is that any non-Ice pokemon will take 1/16 of its HP in damage every turn.  Only a few abilities are affected by Hail- Ice Body pokemon will regenerate at the same rate they would have lost HP if they weren’t an Ice-type, and Snow Cloak pokemon gain the same evasion boost as a Sand Veil pokemon in a Sandstorm.  Castform becomes Ice-type (fortunately for it).

As moves go, Hail boosts Blizzard to a 100 accuracy and gives it a 1/4 shot at piercing Detect and Protect, and the usual three Grass-type recovery moves are all reduced to their minimum of 1/4 HP recovery.  Weather Ball doubles in power and becomes an Ice attack, which is pretty nice and really the only actual benefit to Castform from Hail, since not taking damage is offset by becoming a weak pure-Ice type pokemon.

Because the only pokemon that benefit from Hail are all Ice pokemon (unless you’re willing to let a Water or Normal type take 1/16 damage every turn just to get off a high-accuracy Blizzard) the range of pokemon open to inclusion in a Hail team is unfortunately small, and composed to a large degree of pokemon that have either glaring weaknesses or a general lack of good options to begin with.  In the former category is Abomasnow, who provides effectively unlimited Hail but takes massive damage from Fire attacks and double damage from not only Fighting and Rock moves, but also Flying, Bug, and Poison attacks and is just sort of generally a second-rate tank to begin with.

Theoretically, a grass-type who can plant their roots with Ingrain and soak damage easily would work with Hail, and perhaps Leech Seed gives some potential.  Magic Guard Clefable might work as well, since it’s immune to the Hail damage.  Other than that, though, the list of worthwhile Ice types is small and many of their movepools are as well.  The most notable exception is Froslass, who combines Thunderbolt and Blizzard during Hail to rip giant holes in anything while dodging a lot thanks to Snow Veil (and, presumably, some Brightpowder as well).  Still, any attempt to make a Hail team is going to have to be made carefully, and using it in battle will need a lot of tricks up your sleeves- or else you’ll just lose out to the first thing you encounter that’s on fire.