Does are notoriously territorial. One thing to make sure you establish before starting to bond any Rabbits is that both are in good health. If either Rabbit has even a slight health problem this can make aggression worse or cause a normally affable Rabbit to become somewhat aggressive.
Not having any neutral territory to bond the Rabbits in is going to make things especially difficult.Is your bathroom also a place that is familiar to Buttercup? Sometimes the bathroom is one place a free range House Rabbit has not had access to before. I am NOT suggesting using the actual bath to bond them in, as some people do. I do not agree with ‘stress bonding’ methods. I mean using the actual room to bond them.
Is there a local Rescue that offers a bonding service ? Most will only do so if at least one of the Rabbits is adopted from them, but some might agree to help. Of course it’s only fair that there will be a fee for this. The money will go toward funding the Rescue, it’s not to make any profit.
T.he only other thing you could try is to make one room out of bounds to both Rabbits for a couple of months. During which time you will need to completely blitz the room to try to remove as much of Buttercup’s scent as possible. Change the furniture around too, add a few new items. Do as much as you can to neutralise the area.
Then when you try another introduction make a small enclosure in the room and put Tricky in there first. Leave him in there alone for about an hour, then bring Buttercup in. First scattering some feed pellets around the bonding enclosure. You will need to be prepared to intervene straight away if immediate aggression kicks off. So wear a thick jacket and gloves to avoid getting injured yourself. Do not use anything like a broom to separate fighting Rabbits. IMO this is cruel and can just wind both Rabbits up more.
Or you could first try creating two enclosures next to each other, making sure the dividing barrier does not allow either Rabbit to stick their nose through. It could then get bitten. Try using the ‘living side by side’ method of bonding rather than the immediate full introduction.
The whole process could take months and initially you will need to be able to supervise them 24/7. Even sleeping next to the bonding enclosure. So you will need to factor this into your usual lifestyle.
Some bonding tips here:
Master the art of pairing up rabbits through bonding. Explore expert advice and resources for harmonious rabbit relationships. Start bonding now
rabbitwelfare.co.uk
And if you are really interested in learning about Rabbit behaviour I can recommend these books