Sequence breaking refers to a number of acts that break the normal sequence of events in the Pokémon games. Sometimes it is possible to visit some places out of the normal order, or skip some areas entirely.
Some of these methods are found in normal gameplay, while other methods involve exploiting glitches.
In Pokémon Red and Blue, there are some methods to leave Pewter City through the east exit without defeating Brock at the Pewter Gym.
As a side effect, Blue remains available for the optional battle in Route 22 if Brock has not been defeated. In normal gameplay, defeating Brock would cause Blue to disappear from that route without that battle.
In Generation I only, the player is able to leave Cerulean City early by cutting the tree at the south.
If the player obtains a Pokémon with Cut from a trade and wins the Cascade Badge (which allows the use of Cut outside of battle) at the Cerulean Gym, it is possible to leave Cerulean City early and skip the Sea Cottage as well as the Route 25. The player can also skip the battle against Blue in Cerulean City.
In normal gameplay, the player would battle Blue at the north exit of Cerulean City, then go through the Route 25, and ultimately Bill would give the S.S. Ticket to the player at the Sea Cottage. This also allows the player to exit Cerulean City through the house burglarized by Team Rocket. (The guard stops blocking the door as soon as the player receives the S.S. Ticket.) The player would normally be unable obtain any Pokémon with Cut before going to S.S. Anne and receiving the HM01 (Cut).
It is still possible to return to Cerulean City and battle Blue at any point in the future, even after the player has already defeated him at the Indigo Plateau and became the Pokémon Champion. However, Blue still uses the same team that would be expected in Cerulean City.
If the player skips the Sea Cottage, they will be unable to board the S.S. Anne (which would require the S.S. Ticket) until they obtain the ticket. However, as this requires trading in a Pokémon knowing Cut, they will not need the HM01 from S.S. Anne either (unless they release or trade away the Cut user before getting the Thunder and Rainbow Badges).
It is possible to remain indefinitely with the Pokémon Storage System labeled as "Someone's PC" instead of "Bill's PC" by never meeting Bill.
However, entering the Route 25 is required if the player wishes to obtain the gift Charmander (in Pokémon Yellow only) or the single available TM19 (Seismic Toss).
It is not possible to use this method to leave Cerulean City early in Generation III games, because the south tree is blocked by a Lass's Slowbro until the player obtains the S.S. Ticket.
In Generation I games with the help of Pokémon Stadium 2 and the Transfer Pak, it is possible to completely skip the Rock Tunnel and Routes 9 and 10 by acquiring a Fresh Water, Soda Pop, or Lemonade and entering Saffron City early.
In normal gameplay, the player needs Cut to enter Route 9 and Rock Tunnel. However, if the player uses this method to obtain a drink item early, they can still explore most of the game without having Cut, and obtain almost all Badges, except Erika's Rainbow Badge and Giovanni's Earth Badge.
This can be done by depositing the drink item from a Generation I game at the PC in Pokémon Stadium 2 via Transfer Pak (specifically, the item should be deposited at the Color Case, which is the Nintendo 64 storage space shared between Generation I games). Once the drink item is deposited, it can be withdrawn to another Generation I game later.
This method is normally unavailable in the earlier games Japanese Pokémon Stadium and Pokémon Stadium, because each player has their own item storage, with no option to transfer items between players. However, in these Stadium games, the players are identified by their name and ID. As a result, items can be freely transferred between Generation I core series games that have the same player name and ID.
This method is unavailable when playing the Generation I games at the Virtual Console, because it has no connection with the Pokémon Stadium series.
In Generation I games, there is an oversight causing the Poké Doll to end the battle against the ghost Marowak.
In normal gameplay, the player would explore the Team Rocket Hideout and obtain the Silph Scope to reveal the ghost Marowak that blocks the way to the Pokémon Tower 7F. However, the player can completely skip the Team Rocket Hideout and simply bypass the ghost Marowak by using the Poké Doll. (However, as a side effect, the player would be unable to battle or catch any wild Gastly or Haunter, because the Silph Scope would be normally used to reveal them as well.)
As usual, once the ghost Marowak is gone, the player can talk with Mr. Fuji at the Pokémon Tower 7F and return with him to his house, in order to obtain the Poké Flute. From this point onwards, the player can also enter Silph Co. (the Rocket Grunt stops blocking the way at the entrance)
After using this glitch, it is possible to battle Giovanni out of order: first in Silph Co., then in Viridian Gym, then in Team Rocket Hideout (which was supposed to be the first battle against him). This contradicts Giovanni's dialogue in Silph Co. ("So we meet again!", "I lost again!?") because in this case he never battled the player before. It also contradicts Giovanni's dialogue at the Viridian Gym, where he says that Team Rocket is finished forever, but in fact Team Rocket still remains in the Team Rocket Hideout.
In Pokémon Yellow, it is also possible to battle the Team Rocket trio out of order: in Mt. Moon, then Pokémon Tower, then Silph Co., then Team Rocket Hideout (which was supposed to be the second battle).
In normal gameplay, the player must acquire a Bicycle if they wish to enter the Cycling Road. This requires obtaining a Bike Voucher in Vermilion City and then backtracking to Miracle Cycle in Cerulean City.
If the player attempts to enter the Cycling Road (through the entrances on either the Route 16 or the Route 18) without a Bicycle, the guard blocks the player from entering. This also causes the player to automatically walk one tile to the right, facing away from the Cycling Road. However, due to an oversight, it is actually possible to enter the Cycling Road without a Bicycle, simply by insisting and pressing left while the guard is in the process of blocking the player.
Once this is done, the player will automatically ride a Bicycle as long as they are on the Cycling Road, even if they have never obtained this item in the first place.
In Generations I and III, it is possible to skip the S.S. Anne by obtaining a Pokémon with Cut from another game.
In normal gameplay, the player would obtain the HM01 (Cut) from the captain in the S.S. Anne, and then teach this move to a Pokémon so it can cut the trees that block the way in several areas. However, the player also has the option to skip the S.S. Anne and obtain a Pokémon with Cut from a trade instead.
If the player obtains the HM01 at the S.S. Anne, then this ship will depart indefinitely once the player leaves it. However, if the S.S. Anne has not departed yet, it is possible to Surf on the water tiles around the ship (by obtaining a Pokémon with Surf, as well as the Soul Badge to use this move outside of battle). The player can also reach the ground tiles surrounding the water and see a truck parked there. The truck serves no purpose in Generation I, but has a hidden Lava Cookie in Generation III.
In Generation I, it is still possible to return to S.S. Anne and battle Blue at any point in the future, even after the player has already defeated him at the Indigo Plateau and became the Pokémon Champion. However, Blue still uses the same team that would be expected in S.S. Anne. However, in Pokémon FireRed and LeafGreen, if the player enters Lavender Town without having battled the rival in S.S. Anne, this battle will be permanently unavailable as the rival will not be found in S.S. Anne anymore.
In Pokémon FireRed and LeafGreen, the first trip to the Sevii Islands (where the player is invited by Bill after Blaine has been defeated) is normally available even if the S.S. Anne is still docked at the Vermilion Harbor. The player will also receive the Tri-Pass and be able to freely use the Seagallop to travel between the first three islands. However, once this mission is over and the player returns to mainland Kanto, they will not be able to travel to the Sevii Islands again until the HM01 is obtained and the S.S. Anne leaves the Vermilion Harbor.
In Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!, as obtaining the Secret Technique Chop Down from the captain of the S.S. Anne is a requirement for entering the Vermilion Gym, the ship and the rival battle aboard it cannot be skipped. Unlike in Generations I and III, the harbor is not considered a part of the S.S. Anne and can still be accessed after the ship has left, and the area with the truck can be accessed once the player has learned the Secret Technique Sea Skim. This area now contains a hidden Revive, which renews occasionally.
In Pokémon Brilliant Diamond and Shining Pearl, there is an NPC in Valor Lakefront who blocks the entrance to Route 222 and Sunyshore City until DialgaBD or PalkiaSP has been caught or defeated.
However, if an Egg hatches when the NPC would block the player, then it is possible to ignore him and enter this city regardless.
ncG1vNJzZmiapaGvorzEnaCaZpKquaOtxpqpnZ2eY7umwI6woKShX4iyssHEp5qel5KnsqK3yKee