The prototype colossus is the one in Solomons now unless you got the Prime colossus when twitch did the promo, and just never used it.
all of the legendary pets can do the same things.
Do you NEED it for slayer no.. Is it helpful...yes.. it will pull you to safety if you should almost die, it can alchy stuff for you 1 ever 15 min.. and i think you can choose it to send something to bank also. Many uses.. but there is NO NEED for it unless you just want the extra help.The richest person is not who has the most. It is who Needs the least.