What is the effect of mentos on diet coke?

Mentoes explode in both

Fizzy! Carbon dioxide is released at a crazy rate so the coke normally shoots up into the air while it breaks down the mentos exterior.

it make a big mess of a cola or it could make a puddle

Chocolate

Because when the mentos and coke react, it makes a huge fountain of coke explode out of the bottle and it can look quite cool.