There is a lot of misinformation on the internet about how introductions should be done between chinchillas. The key to developing a strong bond between chinchillas is to cause an immediate bond and avoid stressors that could break the bond.
The very first point that is incredibly important to understand is that long, drawn out introductions are incredibly dangerous! A long bonding process where you slowly introduce the chinchillas through playtime or in a neutral area infrequently is the number one cause for repeated dominance fighting and a lack of bond formation. When chinchillas are brought together and taken apart repeatedly, this does not act like it does for you meeting a new person and forming a friendship. Each time the chinchillas are separated, any work that has been done between them to establish or determine dominance is essentially reset. This means that each time you let the chinchillas play together, they are going to do chasing, dominance humping, and even attacking in order to attempt to establish dominance. If slow introductions are not the way to get two chinchillas to live in harmony, then how do you go about introducing two chinchillas? If getting two or more chinchillas to live together in harmony were as difficult as some facebook groups and websites purport on the internet, breeders would never be able to introduce the pairings we want. Breeders are the chinchilla owners with the most experience in pairing chinchillas and these are the people whose advice you should be seeking in order to properly introduce two chinchillas.
The number one method for introduction is going to be to take the chinchillas you wish to bond and put them into a small carrier together that they cannot fight in. Put the carrier in your car and go for a 30 minute drive. Leave the chinchillas together in the carrier for an additional 4 hours. Once this is done, you can allow them into a cage together with no need to pull them apart and no fear of fighting. This works 99.9999% of the time for introducing two or more chinchillas. The only time I have not seen this work is when it is done improperly or if a chinchilla has been alone for more than 4 years and is too spoiled to accept a cagemate. This is the safest and surest way to introduce chinchillas.
Another method is the cage within a cage method. You take a smaller cage that fits inside of a second cage. Put one chinchilla in the small cage with access to their own food and water and put the second chinchilla in the larger cage around the small cage with their own source of food and water. Allow them to live in these two cages for at least 1 week, 2 weeks is preferable, and when 1-2 weeks has passed, you can remove the small cage and allow both chinchillas to roam freely together.
The last method is called the smoosh method. This method has mild success, but when paired with a car ride as described in the number one method, this can work exceptionally well. The smoosh method does not work on highly aggressive or dominant chinchillas as they have to be highly stressed in order to form a bond and not be hyper focused on asserting dominance. The smoosh method is one where you take two chinchillas and place them into a small carrier or cage together. This cage or carrier must not be tall enough for either chinchilla to stand or move away from each other. It should prevent them from being able to fight with each other or avoid each other.
You have to choose a method that you are comfortable with and that shows high success. Again, slow, long, drawn-out introductions have very low success rates of about 50% and they are more likely to result in the chinchillas fighting and breaking their bond after only a few years. Using either of the first two methods described is going to afford the highest success rates. Chinchillas introduced with these methods have lived together harmoniously for their entire lifetimes which averages 10-15 years.