CCL, I hope I didn't upset you with my frankness about the Ally/Connor situation. There are days when it seams like everything has worked out OK, and then there are days when I wonder what I was thinking bringing another cat into my house.

Is it possible to keep Mr Magoo in a separate room, so he is less restricted than in a cage, and go through the normal slow introduction - swapping scents, and building up to supervised interaction? There must be a lot for him to get used to - new smells, new space around him, new noise, and unfortunately you were at the receiving end of his confusion / frustration.

Space permitting, I would try to have him in a room, rather than a cage - but I don't know your household, so I am not sure if that is possible.

Connor spend 2 weeks in a separate room before any real interaction took place - I am sure the situation here would have been much worse if I had integrated them sooner.

One other thought - did Mr Magoo have a cage-mate at the shelter or was he isolated? If he did, maybe he is missing his friend, if not, maybe he is not ready to share his cage with your other cats, and lashed out at you in misdirected anger???