The question's simple, who do you think is the worst legendary pokemon of all time and why? I'd say that Virizion is the worst because it's a grass/fighting type, which is very kind of sad.

I want to say Phione but I'm not even sure if that Pokemon is a legendary.

I think Moltres is one of the worst legendary's to use. It's move pool is very limited and stealth rock basically destroys it. You are better off using Talonflame who is also a Fire/ Flying type that has the hidden ability Gale Wings.

The worst legendary is definitely Phione. Why do I say this? Well, that's because it has the worst base stats of any legendary. With a base of 80 for each stats, it's stats are equal to that of a Glalie. Also, it can't evolve into Manaphy, even though it comes from a Manaphy and Ditto breeding. That's reason enough for me to say Phione is the worst legendary.

I would honestly have to say Mew. Yeah, its one of the originals and all and its pretty strong at times, but when you go on to have a Pokemon like Mewtwo, Mew just kind of gets pushed to the back and ends up in Mewtwos shadow. It's still good, but its just really bad because there happens to be a version of it that's so much better and that's why I think its the worst.

Out of all the legendary pokemon, I would have to say that the entire Regi family are all pretty lackluster. Out of all of them though, Regigias is the worst by a landslide (get it? Because it towed continents together? No? Fine...). It has excellent stats all across the board, but it has to wait an agonizing five turns before it can attack at full power. Seriously, Slow Start is arguably worse than Slaking's Truant ability. This is a major setback because this current metagame heavily focuses on one hit kills and sweeping, so attacking at half power for five turns is pretty embarrassing for a legendary pokemon with an attack stat of 160.

Another setback Regigigas faces a lack of recovery moves aside from Drain Punch. Even a high base 110 HP pokemon will eventually need to recover, especially Regigigas because of its halfed power. Overall, I'm really disappointed in its ability and moves. It could've been so much better if it hadn't been for those two things. I hope it gets a Mega/Primal evolution/reversion because it doesn't see much use. The same goes for the other Regis. All of them have ridiculous defenses, but pathetic attack stats and a lack of good moves and abilities. These are some of the least used pokemon out there for these reasons.

The standard response is probably Phione but to deviate I would have to go with Regigias, probably the Pokemon that is the biggest waste of potential in terms of usability of any Pokemon.

Slow start halves it's monstrous attack which is really supposed to be its standout stat and it's decent speed for five turns which is bad because the way Pokemon is structured now a battle will 95% of the time end before slow start can wear of even ingame. It's not a good thing when a legendary Pokemon ends up being weaker than the Pokemon it's supposed to be the master of especially when this is arguably supposed to be one of the most powerful legendaries in the game but that's pretty much what happens here.

Hence there is really no good reason to use this Pokemon, maybe eventually gamefreak will realize their mistake and cut it down to just one turn after it's sent out... but most likely not.

I share the dislike for Phione and Regigigas, but I also have to go with Deoxys. While it can have a nice moveset, most of its forms aren't actually worth using. 

Normal form? Has 50 HP, defense and special defense, so it will go down with ease. Of course, 150 speed isn't easy to beat, and that 150 attack and special attack are fearsome, but still it means taking big risks.

Attack form? Has even lower defenses but increased attacks. Again, not easy to be outclassed in speed, but even easier to fall down should it be hit.

Defense form? Lowered speed and attacks, but strengthened defense. This one won't go down easily, but it won't beat an opponent quickly either.

Speed form? Balanced attacks and defenses, but incredibly high speed. Probably the only useful form, because 90 attack and special attack is decent when it's coupled with 95 defense and special defense. Still, 50 HP make it very fragile.

Normally, Legendaries have extremely high stats, but seeing one with such poor values no matter how high are the rest doesn't pay off the effort of catching them with the low catching rate they usually have. Too bad, because Deoxys has a really nice design, probably one of the best looking Pokemon in my opinion.

zanderlex : I'd have to disagree. Mew may have less overall than Mewtwo, but a 100 base on each stat makes it one of the most unpredictable Pokémon when used against others (Celebi and a couple of other Pokémon share this spread). Moreover, Mew is one of the only, if not the only, Pokémon to be able to use both Bulk Up and Calm Mind, making it a great setup Pokémon. Its move pool also gives it the possibility to take down almost any type, especially if its a speedy sweep Pokémon with something like an Expert Belt.

On the other hand, you can instead make it a tank and eat away at your opponent slowly. Although I feel that Celebi can do this better thanks to Giga Drain, Mew is still more than capable of doing this.

It's hard for me to say exactly what the worst legendary is, but I think I'd have to go with Regigigas, as well. Slow Start usually means that a single smart switch out from the opponent to avoid getting KO'd by Regigigas' stellar attack (Chansey with Eviolite, for example; while not the best example because of its lacking attack power, it can still then use Toxic on Regigigas and make it eat away at its HP), and you can essentially take it down. At best, it usually trades off KOs with the opponent, unless the opponent happens to have no counter against it (and almost every good team has a great Defense wall). And personally, I also hate using slow Pokémon. <insert Sonic "ur 2 slow" meme here>

I think that Regirock is the worst legendary. All 4 of the Regi Pokémon are garbage, but Regirock, in my opinion takes the cake for the worst. It is weak to so many types and is only good against Fire, Ice, and Flying. It serves no purpose outside of battle either, as it is just there so you can fill your Pokedex. 

My personal opinion I think the worst is jirachi. I know its probably not the worst I just really don't like that one but that's my personal opinion.

My least favorite legendary is probably Diancie as of now. The Gen 6 mythicals so far are meh, but Diancie is the worst. I don't really see a point of her existing besides having a Fairy type mythical Pokemon.

If I had to pick,I would choose Diance.The story is a little good,But I just hate the Pokemon.Whenever I got it,(X/Y)It was horrible.Also,Not a big fan of Mega Diance.

Arceus. Sorry but I prefer every other legendary over arceus for his move set because I suck at using it and I suck at bringing out his full potiential...So...who wants a arceus?
Truth be told i am being completely serious here i suck at owning one and i think i could raise the other legendarys into better fighters than i could raise arceus. 

I personally think Diancie is the worst legendary. I found her rather annoying in the movie, and... she really serves no purpose. For example... Arceus, Giratina, Dialga, Palkia created the universe.. Kyogre filled the sea, Groudon formed land, Regigigas moved continents, Azelf, Mesprit and Uxie gave knowledge, willpower and emotion to all living Pokemon, etc. All other legenderies have a purpose, but Diancie is just there as some kind of mythical fairy. I mean, I like her design. He mega evolution looks beautiful too... but quite useless. I wouldn't use her in battle too, mainly because of her very low speed and HP. (But has good defence) 

gamerforlifeforever2 :
Phione isn't actually a legendary, which could explain it's low stats ^^ 

Toothie : it's technically classified as a legendary pokemon

That said, Phione has its uses competitively. I'd say Virizion is pretty weak compared to other legendaries. Its stats aren't good and its typing is horrible. Plus the design is easily the worst out of the trio (but still better than keldeo's lol).

I can't decide which one out of Mespirit, Uxie, or Azelf is the worst Pokemon. So I'm gonna have to say that Mespirit is the worst Pokemon only because of its location in the game and its design. Personally I don't think it's worth the effort to catch any of them unless you want bragging rights.

Meh... Mespirit, Uxie, and Azelf were all so dang weak, it was kind of pathetic for the Diamond and Pearl games. 

They had awful stats, are even if they aren't the worst legendaries, they are without a doubt the worst set of 3 from any generation. 

Plus, they were impossible to catch, which makes the payout for their god awful stats even less. I don't even understand who thought giving three legendary Pokemon with that low of stats even made sense, but that's just my opinion. 

If I have to choose what one I don't like, mine would be Regigigas. I love the Regis and all, but Regigigas is annoying because of It's Slow Start ability making it very easy for it to die before it gets going.

Heatran. Its the only legendary pokemon with a gender, Its in one game, and all of his/her moves suck

I've got to go with Regigas. It's a beast of an attacker, but its ability, Slow Start, not only halves its speed, but takes away the potential for any other ability to be useful. Almost no pokemon is going to survive three or four turns, much less five, unless they can sweep very effectively, and not a lot of pokemon can do that when they're as slow as Regigas, especially a normal type with no resistances and a weakness to the fighting type.

Plus, in general, it has a bad design in my opinion and, being a normal type, can't get a STAB out of anything that isn't weak against commonly used and encountered types such as the steel, rock, and fighting types.

And then, there's the three lake pokemon, all of whom deserve an honorable mention. Their awful stats and the insane difficulty of catching them made them horrible.