Substitutes are potential houseguests that were put on a queue. If a houseguest that was accepted into the cast decided to back out between the day they get notified and the day the game begins, a replacement would be made from the queue. The queue usually contains 3 people and has been around since the first season.
Charmander was asked to replace Quilava after he quit. However, the offer was declined and the season went on without a replacement.
Shiny Butterfree (katanabombs123) and Vulpix (Ari Suiri) were on the waiting list for being casted. Despite this, Gardi from Pokemon Big Brother 1 came in to play instead, possibly because it was already after Week 1. While this was one of the experimental first seasons, Host decided to create a new rule of no substitutes after the first eviction.
This season was the first with an actual casting call. Because of this, casting created the first queue system where at least 3 players would be put aside as replacements.
Cinccino and Starmie from Pokemon Big Brother 1 were supposed to be cast as a returning duo instead of Auran and Lyra. However, casting did not know their contact information at the time.
Not much is known about who was in queue in Season 4.
This season was the first to make a substitution before the game. A Whimsicott went through the interview process, but when they were given a notice that they were casted and asked to respond, they never responded. Cody the Floatzel was substituted in.
Cyndaquil and Blitz were meant to be the Season 2 and Season 4 representational coaches of this season. However, due to both declining, Yellow Wailord and Jay were asked. Jay also declined, finally leading to Illusion being cast as the Season 4 representational coach.
During the first few days of this season, contact with player 8-track the Porygon was lost due to the player experiencing real life difficulties. Therefore, Shadow the Darkrai was substituted in.
Despite a controversial player, Noah the Snover / Gundam the Sableye, from Pokemon Big Brother 2 and Pokemon Big Brother 5 respectively, was supposed to be apart of the Twin Twist of this season, though more directly as Nick & Phil (Big Brother Canada 4) rather than being tricked into believing it would be like Liz & Julia (Big Brother US 17), mostly because the "twins" were different Pokemon. Noah would have played as a Grovyle, while the brother was Cacturne. This twist got altered due to Cacturne not responding back whenever being reached out for casting.
While it was known that Noah would have been a Grovyle, this could also mean another potential cast member was replaced by Riou the Biker Grovyle. Speculators say that Riou was suppose to be hit with the "Pokemon Change" twist, but it is unconfirmed.
Terri the Shiny Miltank from Pokemon Big Brother 6 was meant to return as a new character Ray Cheesy the Black/Red Wingull. As contact was lost and they could not be interviewed, casting immediately went to Shell the Carracosta from Pokemon Big Brother 5 instead where he ended up playing as new character Swif the Archeops.
Zack from Pokemon Big Brother 3 was asked to return for this season and originally accepted. However, due to a vacation he had planned, he had to let the hosts know that he could no longer join in.
Lydia from Pokemon Big Brother 7 was also asked, but she declined.
Rex and Kandy became their replacements.
- So far, most replacements have gotten evicted either pre-jury, or have not gone to jury their season. The only exceptions are Auran and Rosie & Lisa. Gardevoir (PBB2), Lyra (PBB3), and Swif (PBB7) became finalists and were not in the jury.