Before you choose which pokemon you want your Gijinka to be, you must know what pokemons may not be taken. There aren't many, but they are still necessary to know.
The limitations are as follow:
-No Legendary pokemon are allowed. Last evolution of Pseudo-Legendary pokemons aren't allowed either.
-No pokemon taken twice may be taken again.
-Keep in mind that no Gijinka may "evolve", but also that stats are balanced.
List of (Pseudo)Legendary pokemons:
Generation 1: Zapdos, Articuno, Moltres, Dragonite, Mewtwo, Mew
Generation 2: Entei, Raikou, Suicune, Ho-oh, Lugia, Tyranitar, Celebi
Generation 3: Regirock, Regice, Registeel, Metagross, Salamence, Latias, Latios, Groudon, Kyogre, Rayquaza, Jirachi, Deoxys
Generation 4: Azelf, Mesprit, Uxie, Dialga, Palkia, Giratina, Darkrai, Cresselia, Manaphy, Phione, Garchomp, Heatran, Regigigas, Shaymin, Arceus
Generation 5: Victini, Hydreigon, Cobalion, Terrakion, Virizion, Keldeo, Tornadus, Thundurus, Landorus, Reshiram, Zekrom, Kyurem, Meloetta, Genesect
List of taken pokemons:
006: Charizard (x1)
025: Pikachu (x1) *
026: Raichu (x1)
148: Dragonair (x1)
202: Wobbuffet (x1)
217: Ursaring (x1)
235: Smeargle (x1) *
257: Blaziken
285: Shroomish (x1)
329: Vibrava (x1) *
335: Zangoose (x1)
355: Duskull (x1) *
362: Glalie (x1)
429: Mismagius (x1)
433: Chingling (x1)
571: Zoroark (x1)
587: Emolga (x1)
600: Klang (x1)
620: Mienshao (x1)
*: The player has shown no recent sign of activity.