Gamers of "Pokemon GO" know so well that there are certain Pokemon that are very difficult to catch. In order to successfully catch these Pokemons, one will need to have stronger Pokeballs and much more raz berries.
According to a Reddit page by Silph Road, these Pokemon that are very difficult to catch in "Pokemon GO" are based on their capture rate and iTech Post sums it up in an article.
Four Percent Base Capture Rate Pokemon
Those Pokemons that did not undergo any evolution in the game "Pokemon GO" are easier to catch. And for those evolved Pokemons, trainers can waste a lot of time capturing it. Blastoise, Dragonite, Venusaur and Charizard are Pokemons that are in their third level. These Pokemon have a capture rate of four percent which could be hard to catch using a regular Pokeball.
To have the best chance in catching these strong Pokemon monsters in "Pokemon GO", trainers will need to have a Masterball to have a 100 percent chance of catching these tough Pokemon creatures. But it is said that it is very difficult to have a Masterball which leaves you with Ultraball as a replacement if you do not have one.
Eight Percent Base Capture Rate Pokemon
Pokemon creatures in Pokemon GO" with eight percent base capture rate are much more difficult to catch than those Pokemon with four percent capture base. There is only one Pokemon that is fully evolved with eight percent capture base, which is the Gengar Pokemon. First evolved Pokemon creatures with eight percent capture rate include Raichu, Charmeleon, Gyarados, Ivysaur, Ninetails, and Dragonair.
Trainers can also use Dusk Balls in "Pokemon GO" which can increase your chance up to four times of the catch rate if the Pokemon is caught in caves or at night. While those Bug and Water Pokemon can be caught using Net Ball which increases the capture rate three times.
High Flee Rate Pokemon
High flee rate Pokemon is also very difficult to catch in "Pokemon GO." Pokemon Abra, which has a 99 percent flee rate can only provide one chance to be caught. If the trainer failed to do so, they will unlikely have a second chance to capture it.