My group and I are playing ToA, my warlock just died and I need a replacement. I've been changing my mind a lot so I asked my group what I should go, they said a full caster. As a result, I figured I would try and build a transmuter wizard, a concept I had liked. Any help making a feasible transmuter build would be great. Tips on race, feats, stat arrangement, multiclassing and playstyle would be appreciated. Thanks

Okay, I think that there is a lot of play as for what is "good" to get as a Transmuter. My main recommendation is to focus on support and utility spells such as Bones of the Earth, Tiny Servant, Create Humunculus, and Identify. In conjunction with you Transmuter's stone, you will become a valuable support character (While still throwing a mean Fireball).

 knock enlarge/reduce and levitate are incredible low level utility spells. minor alchemy is very useful too, perhaps for turning metal hinges into wood a sawing them off. or turning a wooden shaft into metal to pry a wagon up etc etc