Okay some bakugan have attribute changes, so to understand what elements they change to and from here's a list of all the attribute changes.
Preyas:
Pyrus Preays: Pyrus, Darkus, Ventus
SubTerra Preyas: SubTerra, Aquos, Pyrus
Haos Preyas: Haos, Ventus, SubTerra
Darkus Preyas: Darkus, Pyrus, Haos
Aquos Preyas: Aquos, SubTerra, Darkus
Ventus Preyas: Ventus, Haos, Aquos
Diablo/Angelo
This isn't really a change but it's the other elements that Diablo/ Angelo will come in when your Preyas evolves. The elements are the other two in the triangular relation and the base attribute of the Evolved Preyas.
Pyrus Preyas Evolves: Diablo=Aquos/Pyrus, Angelo=Haos/Pyrus
SubTerra Preyas Evolves: Diablo= Darkus/ SubTerra, Angelo= Ventus/SubTerra
Haos Preyas Evolves: Diablo= Pyrus/ Haos, Angelo= Aquos/ Haos
Darkus Preyas Evolves: Diablo= SubTerra/ Darkus, Angelo= Ventus/ Darkus
Aquos Preyas Evolves: Diablo= Pyrus/ Aquos, Angelo= Haos/Aquos
Ventus Preyas Evolves: Diablo= Darkus/ Ventus, Angelo= SubTerra/ Ventus
Brontes:
Pyrus Brontes: Pyrus/ Subterra
SubTerra Brontes: SubTerra/ Haos
Haos Brontes: Haos/ Darkus
Darkus Brontes: Darkus/ Aquos
Aquos Brontes: Aquos/ Ventus
Ventus Brontes: Ventus/ Pyrus
Elfin:
Pyrus Elfin: Pyrus/ Ventus/ SubTerra
SubTerra Elfin: SubTerra/ Pyrus/ Haos
Haos Elfin: Haos/ SubTerra/ Darkus
Darkus Elfin: Darkus/ Haos/ Aquos
Aquos Elfin: Aquos/ Darkus/ Ventus
Ventus Elfin: Ventus/ Aquos/ Pyrus
Tripod Theta:
Pyrus Tripod Theta: Pyrus/Ventus/ SubTerra
SubTerra Tripod Theta: SubTerra/ Pyrus/ Haos
Haos Tripod Theta: Haos/ SubTerra/ Darkus
Darkus Tripod Theta: Darkus/ Haos/ Aquos
Aquos Tripod Theta: Aquos/ Darkus/ Ventus
Ventus Tripod Theta: Ventus/ Aquos/ Pyrus
Tripod Epsilon:
Pyrus Tripod Epsilon: Pyrus/ Darkus/ Aquos
SubTerra Tripod Epsilon: SubTerra/ Aquos/ Ventus
Haos Tripod Epsilon: Haos/ Ventus/ Pyrus
Darkus Tripod Epsilon: Darkus/ Pyrus/ SubTerra
Aquos Tripod Epsilon: Aquos/ SubTerra/ Haos
Ventus Tripod Epsilon: Ventus/ Haos/ Darkus