Please don't include legends because they will be there and I like to play nuzlockes with no legends :). Also don't include post game Pokemon only include the original 146 (this number is exclusive of the legend and mythical).
Kadabra / Alakazam Availability: Early Stats: Above average Movepool: Average Additional Comments: Psychic typing is very useful for all the Poison-types that are in the game. High Special Attack and Speed stats net quick and easy KOs. However, needs to be traded to fully evolve, which requires two Gameboy Advances/SPs and a link cable or wireless adapter. Nidoking Availability: Early Stats: Average Movepool: Very wide Additional Comments: Has well-distributed stats and learns a vast amount of TMs and in-game move tutor moves. Clefable Availability: Early Stats: Above average Movepool: Very wide Additional Comments: Learns a vast amount of TMs and useful moves upon level up, and is very bulky both physically and specially. Can also be evolved as soon as it is obtained with a Moon Stone. Venusaur Availability: Beginning Stats: Above average Movepool: Shallow Additional Comments: Learns 3 useful status moves and has a useful Grass-typing in the beginning of the game. However, there are many Poison-types in the game, which both of Bulbasaur's STABs are not very effective against.
Kadabra / Alakazam Availability: Early Stats: Above average Movepool: Average Additional Comments: Psychic typing is very useful for all the Poison-types that are in the game. High Special Attack and Speed stats net quick and easy KOs. However, needs to be traded to fully evolve, which requires two Gameboy Advances/SPs and a link cable or wireless adapter.
Nidoking Availability: Early Stats: Average Movepool: Very wide Additional Comments: Has well-distributed stats and learns a vast amount of TMs and in-game move tutor moves.
Clefable Availability: Early Stats: Above average Movepool: Very wide Additional Comments: Learns a vast amount of TMs and useful moves upon level up, and is very bulky both physically and specially. Can also be evolved as soon as it is obtained with a Moon Stone.
Venusaur Availability: Beginning Stats: Above average Movepool: Shallow Additional Comments: Learns 3 useful status moves and has a useful Grass-typing in the beginning of the game. However, there are many Poison-types in the game, which both of Bulbasaur's STABs are not very effective against.
My comments: Best against the first 3 gym leaders (super-effective against Brock and Misty and resistance to Surge).
Hope this helps. Source