Who's that Pokémon?
Bash 1182 chars
read n;echo {Bulba,Ivy,Venu}saur Char{mander,meleon,izard} {Squi,Warto}rtle Blastoise Caterpie Metapod Butterfree Weedle Kakuna Beedrill Pidge{y,otto,ot} Rat{tata,icate} {Sp,F}earow Ekans Arbok {Pika,Rai}chu Sands{hrew,lash} Nido{ran%\(f\),rina,queen,ran%\(m\),rino,king} Clefa{iry,ble} Vulpix Ninetales {Jigglyp,Wigglyt}uff {Zu,Gol}bat Oddish Gloom Vileplume Paras{,ect} Veno{nat,moth} Diglett Dugtrio Meowth Persian {Psy,Gol}duck Mankey Primeape Growlith Arcanine Poliw{ag,hirl,rath} {A,Kada}bra Alakazam Mach{op,oke,amp} Bellsprout {Weepin,Victree}bell Tentac{ool,ruel} Geodude Graveler Golem Ponyta Rapidash Slow{poke,bro} Magne{mite,ton} Farfetch\'d Dod{uo,rio} Seel Dewgong Grimer Muk {Shelld,Cloyst}er Gastly Haunter Gengar Onix Drowsee Hypno Krabby Kingler Voltorb Electrode Exeggut{e,or} Cubone Marowak Hitmon{lee,chan} Lickitung {Koff,Weez}ing Rhy{horn,don} Chansey Tangela Kangaskhan Horsea Seadra Goldeen Seaking Star{yu,mie} Mr.%Mime Scyther Jynx Electabuzz Magmar Pinsir Tauros Magikarp Gyarados Lapras Ditto Eevee {Vapore,Jolte,Flare,Poryg}on Oma{nyte,star} Kabuto{,ps} Aerodactyl Snorlax Articuno Zapdos Moltres Dra{tini,gon{air,ite}} Mew{two,}|tr %\ \ \\n|sed $n!d
PHP 919 (925) bytes
As with Peter Taylor's answer, I also cannot post my solution directly, so instead i'll post a program that generates it:
<?php
$data = <<<EOD
PD9mb3IoJG89J5SWUHYPaY6dSs/pjsJBMS1pRDc1yZ3AUcQkNcnZsYIkJDXtpa4UB4mOMNH8zbDbcDhcKD
VYu89cFyjRlBm8GSjMiFSxCNHitpn8Kdi43B+XUkX2gVjN8LQEmEkF5D2zE9gbTD3z6djUJQAVFXwlXV/o
kVwnsV1rW5J9zpssN3JXdW5LjAS3DYTcBtV/YUdtoAfGC+ztsoc1LxQamD5lmQMaes37flJcGvg7CdkS+s
1bhZLjAQQtmL5tS3rN+2eS7LeROnX9nOCRRWhRQhFkBDSN0igwMUwem4BNYVrkxZuAzUEiRDG+KFODVqV0
KDAvpLM747wC0AwYUVkELsVsBA5vyThUQQtiKFRBK6EYnBC7oMiAkJtYbXOZk9scdPF3hTJEh7hhZ4yDEG
FHzJ1vSfxkDVkd8fz+u6ConHVH7Y3SHFtgq20M22ALpO40xMC9vmictX6lf+2VfqV1EBctRRwZ38RceT3E
G2l5PcTVTFahWEdGGYhjKSwy5lBYAn944VmhWNQRkvXDw5SAkpV/URm0SZPBOPweZUGwDlODERHEwt0VfK
X9WG+kp9tbe+d8oLvu1uw9+6ExyFwZe6LogoTF7oG3RCiUm0GTcJsmcyxJmdRR68Oi7P4NmQ6ZlwxE8djR
DtfANTjRZBOvWE281RLRDtPJY05E4k10BkvfCRwNLKssXh4GHB+SgBFEwsDbHsSxMdhmCBExsfvZKLzEEY
uZ26SXfutBOR1rezc8/XmT6HkcHciTBwTSxD1cJ+XBcmyjis2S7ClZLZJMTG2bngTs7VtCN3VSaQUAcuPQ
VR9yY0+ntSTcnhcdZ4n4JtzDwPHZJEl9pZJsONV96ad1jpV5eVhpldF8r7WcMeRd8hSxMXjVEcZEPZsdLg
SSd+4kNY7L7Bkbdy10VDVuJdtfGOyG7yydwJux2SFcAiz7QSIEa8BxAoQIFUFCRJt+G6KkoZ3d8fzBPZhO
xG2eaIwfvrGb54zZ7mgfGPA0Qp6I5NSund9SSw5MUD8M0wAmzywmSF2N/CZbw8V1JEZF42LIXJmLeIM5uU
wnOzc4OD4kbjspJGY9c3BsaXQonywkeC49Y2hyKDMxJiR2PSsrJGklOCUzPzgqJHZeb3JkKCRvWyRuKytd
KTokdj4+NSleiyk7ZWNob35zdHJ0cigkZlsrZmdldHMoU1RESU4pXXygLICEgYOCLNfY1tHfKTsNCg==
EOD;
print base64_decode($data);
?>
Sample I/O:
$ php generator.php > out.php
$ echo 12 | php out.php
Butterfree
$ echo 32 | php out.php
Nidoran (m)
$ echo 83 | php out.php
Farfetch'd
$ echo 122 | php out.php
Mr. mime
$ echo 151 | php out.php
Mew
How it works (spoiler):
This code operates on the observation that there are only 32 unique characters, including a separator - if you're not counting capitals. This immediately implies a 5:8 encoding; only 5 bits are needed to represent each byte.
I accomplish this in the following manner:
++$i%8%3
When this value is non-zero, a new byte is read, and when zero, the next byte is generated from the previously read bytes. The 3rd, 6th, and 8th byte are generated in this manner, and then the process repeats.
The bit distribution follows accordingly. If for example you wanted to produce the string:
abcdefgh
The bits for each are distributed among the 5 source bytes in the following fashion:
hccaaaaa|cccbbbbb|hffddddd|fffeeeee|hhhggggg
After generating c, only the top most bit of h remains, after generating f, the top two bits of h remain, and after reading g, h remains in its entirety (I save a few shift operations by using xored values instead, for example the value I load for the second byte is the value I want xor a<<3, but that's the gist of it).
This produces characters on the range of [0,31]. By xoring by any character on the range [96,127], all characters will be mapped to that range (I chose 116, because it resulted in the least amount of escape sequences). After that, it's a simple matter of translating the 5 characters that don't belong there with their appropriate replacements, and capitalizing the first letter. This code requires three bytes to do so: oring the (previously generated as such) bit inverted string with char 160, and then bit inverting back. A small caveat: the second m in 'Mr. mime' is not capitalized by this method. This could be repaired by replacing the method described above with the ucwords() function, at the cost of 6 bytes, resulting in a code length of 925, instead of 919.
J (93 + 787 = 880)
Edit: other capitalisation method that capitalizes 'Mr. Mime' correctly.
Can probably be shortened, I've almost never written J before. It works on a similar principle as the PHP example.
You need the 'p' file in the same directory as you run this, the file can be downloaded from: http://frankenstein.d-n-s.org.uk/p. It is 787 bytes.
u:p-32*96<p*|.!.1[32=p=.(}.p#~(".1!:1[1)=+/\31=p=.#._5>\,#:a.i.1!:1<'p'){(97+i.26),a.i.'.()'' '
The file is encoded in a five-bit format, as follows:
0-25: A-Z
26: .
27: (
28: )
29: '
30: <space>
31: separator
The file also starts with a separator, to make the list 1-based.
The J code works as follows:
(97+i.26),a.i.'.()'' ': a string where the index N is the ASCII character{: select from this list the values generated by the expression below1!:1<'p': read the 'p' file,#:a.i.: get the file as bits_5>\: group the bits in groups of fivep=.#.: transform each group of bits into a number and assign top+/\31=p: a list of the size ofpwhere each value N means the value at that position inpbelongs to the N-th pokemon.(".1!:1[1)=: read a number from the keyboard and see where inpthe characters for that pokemon are.}.p#~: look them up inp, and remove the first item (which is the separator).p-32*96<p*_1|.(!.1)32=p=.: Assign the output topagain, and subtract 32 frompwherepis bigger than 96 and to the right of a space. Which is cumbersome. According to the J documentation there should be acapitalizefunction but it's not there on my system.u:: look them up as unicode.