Originally Posted by Fat Huntofthelion
I think Jellicent's biggest issue is that it's typing overlaps with the two best spinners in the metagame, Starmie and Tentacruel, which makes it hard to fit into teams. It's also kinda iffy at spin blocking because it can't beat Tentacruel one on one very often and Starmie can do a fair amount of damage to it on the switch in. It's not a bad check to rain teams, especially since it handles Keldeo really well, and it's always going to be annoying to deal with because of it's stats / ghost-typing / water immunity / scald / recover / taunt, but it's not as good as it used to be both because it can't really fill the roles it needs to to be useful to a team and because defensive pokemon in general aren't super productive in this metagame. That said, I used Jellicent on one of my more recent teams and enjoyed having it around because it can at least block the rapid spin and switch out, it's great against Keldeo which my team had issues with, and I love having something that can safely switch into scald. Definitely give it a try but don't be surprised if it's underwhelming.
Don't worry, I'm not going to use Starmie; I definitively disagree that Forretress is meh on sand teams. It is definitively a good choice over Starmie for two reasons; because it can also setup Stealth Rock by itself, and has Volt Switch to mantain momentum. A specially defensive is generally the best to use on sandstorm, as it doesn't fear Water-type attacks as much as it would otherwise.
Back to Jellicent, I am thinking of running her mainly because of her supporting options and typing (seriously, Jellicent has one of the most amazing typing on the metagame, combined with her Water Absorb ability; you have a pokémon that resists Fire, is immune to Water and Fighting, resists Bug and resists Ice! It actually brings a lot of defensive synergy to many teams that don't run too many Water-types)
It's a shame that Jellicent is mostly going to be defensive, because its fantastic typing would be amazing if Jellicent had the stats to go offensive.
Unfortunately I think that the 5th generation is mostly lacking versatile Ghost-types; most of them have problems that prevent them from being good on nearly all teams, which is a shame because Ghost is an amazing type to have. Jellicent is a defensive pokémon for the most part, Gengar is frail, and both can't really defeat Starmie, a common spinner. The worst thing that Game Freak made has taking out Rotom-A's Ghost typing, as Rotom-A was the most versatile Ghost-type that existed. It could go offensive or defensive. Rotom-W, for example, would be the most versatile and best spinblocker on BW OU, as it is already very versatile without its Ghost typing.