Most Phsycally changed in evolution.

[vauny-vaun]

whihc pokemon changes the most (apearence wise not stats) when it evolves. i think remoraid to octillery is a pretty huge change.

what about you?  

[Andy1989]

Magikarp -> Gyarados and Feebas -> Milotic are pretty big changes too...But that's mostly stats...Surskit -> Masquerain is kinda big too...It gains wings and loses legs...And kind of the caterpillars too...But that's realistic.  

[Vickicat]

Dragonair to Dragonite. Dragonite looks so different from Dratini and Dragonair.  

[Andy1989]

Vickicat

Dragonair to Dragonite. Dragonite looks so different from Dratini and Dragonair.

*kills himself for forgeting Dragonite* How could I?! gonk *stabs* But yea...They have a huge change. goes from snake-type thing to dragon.  

[Jazzfox]

Trapinch to Flygon o_o I dun care if it has a pupus stage; how does something that freaking ugly turn into FLYGON!?!?!?!

::Cough...::

Yush; anywhoo... I'd maybe more settle with Feebas ---> Milotic; at least Magikarp/Gyarados share the same shape of mouth and fins lol :3  

[Panda.Ba]

I think that Kabuto>Kabutops is a pretty huge difference. It starts out as this little round disk that makes you wanna go play frisbee, and then it's a big mofo with big sickles and long legs that makes you wanna run back to yo' momma. xd

Sentret>Furret, Chinchou>Lanturn, Togepi>Togetic, Sunkern>Sunflora, Pupitar> Tyranitar, Anorith>Armaldo, Spoink>Grumpig, and Shelgon>Salamanche are also pretty big, in addition to the ones other people said.

But I think that the one that changes the most is Clamperl. Both of the evolutions you can choose for it are incredibly different. Clamperl is a little round ball (it's a pearl, duh) and it's evolutions are eels. In Earth's wilderness, these two have NOTHING to do with each other, let alone LOOK like each other. It might make sense if Clamperl evolved into a big clam, but it doesn't. It goes eel. How much more illogical can you get?

And Dragonair>Dragonite does make sense, even though they don't look like each other. The two form represent two different types of dragons from two different cultures. Western dragons look more like Dragonite (with some alterations, obviously) and Dragonair/Dratini is supposed to be a simplified version of Eastern dragons (they're Eastern dragon minus the legs/whiskers/etc). So it isn't as much of a stretch as it seems.  

[oGolem]

From a structurist point of veiw, I always thought Machamp was a jump--gaining a pair of arms? A *second* pair of arms?!--but I also think anything that goes from quadruped to two legs, like Lairon, Nidorino/Nidorina, and Rhyhorn is a bit of a jump. One that really stands out to me is Chinchou to lanturn, as it changes overall body shape, gains a tailfin--and a huge mouth--changes its eyespots to eyes... Yeah, that one gets my vote.  

[Zeek Slider]

CPanda

And Dragonair>Dragonite does make sense, even though they don't look like each other. The two form represent two different types of dragons from two different cultures. Western dragons look more like Dragonite (with some alterations, obviously) and Dragonair/Dratini is supposed to be a simplified version of Eastern dragons (they're Eastern dragon minus the legs/whiskers/etc). So it isn't as much of a stretch as it seems.

Western Dragons look more like Charizard really. Dragonite is what they have become thanks to American Perversions (I plan on naming one Puff thanks to that marijuana song).

Eastern Dragons look more like Gyrados with legs.  

[Inazuman Frash]

Surskit to Masquerain?  

[Panda.Ba]

ZeekSlider

CPanda

And Dragonair>Dragonite does make sense, even though they don't look like each other. The two form represent two different types of dragons from two different cultures. Western dragons look more like Dragonite (with some alterations, obviously) and Dragonair/Dratini is supposed to be a simplified version of Eastern dragons (they're Eastern dragon minus the legs/whiskers/etc). So it isn't as much of a stretch as it seems.

Western Dragons look more like Charizard really. Dragonite is what they have become thanks to American Perversions (I plan on naming one Puff thanks to that marijuana song).

Eastern Dragons look more like Gyrados with legs.

Well, I said that there were alterations.  

[Toko Ojin]

I have to agree with the set of trapinch to flygon...WTF!? gonk I goes from looking like the lamest looking ground or bug pokemon ever with a psycho ability that makes it annoying to run into and as capable as diglet at killing most electrics to a frikin dragon! eek

Other weird ones I was surprised by were:

Dragonair->Dragonite
The mid stages of Tyrannitar and Salamence, Pupitar and Shellgon...
Diglet->Dugtrio
Shroomish->Bellroom
Clamperl->WTF?!?!zOMG!!!11!1one!!1!
Tyrouge->Hitmontop

I have to say that of these, the EASY winner of evolution nonsensicalness is Clamperl! neutral  

[Load Chaud]

[ Message temporarily off-line ]  

[Nethilia]

Changing form a very ugly little fish to a very prettly long one is quite a change (Feebas -> Milotic) and from a little orange fish to a big blue dragon like creature (Magikarp -> Gyrados) is quite a change.  

[dorkus-malorkus]

Mareep / Flaafy --> Ampharos, ja know.Goes from sheep.. to.. something else. What would you call that, anyway? Oh well.
Wooper --> Quagsire. Talk about limb and body change.
Poliwhirl --> Politoed. There's.. like.. nothing similar between these two.
Psyduck --> Golduck. 'Nuff said.  

[Zeek Slider]

dorkus-malorkus

Mareep / Flaafy --> Ampharos, ja know.Goes from sheep.. to.. something else. What would you call that, anyway? Oh well.

Best I can determin is that it is a "naked" sheep with all the fleese shaved off.