Rolling 1d12, and then 1d20 when the result is 12

I would like to implement some roll dice logics, but can't find a way to do it using Roll20 engine. Here is what I would like to see : roll 1d12 and get the result, except if the result is 12, in which case, roll 1d20 and then take that result if it is above 12. Would someone have an idea how to do that (or know it to be impossible, I would stop searching...)

I believe that most things that require conditional logic (if this then that) need to be an API script.

I think you may be able to achieve that with some roll template if you're using a custom character sheet

As noted, the only way to do that is through the API or a rolltemplate (the clunkiest solution). One other solution is a rollable table, with numbers 1-20, with numbers 1-11 having weights of 20, 12 having a weight of 12, and 13-20 having weights of 1. This gives you the same odds as the system you described. Failing that you can just roll them both, the d20 and d20, and manually take the d20 if it is higher and the d12 is a 12.

[[[[d12>12]]d20]]

The problem with that is if you roll less than 12 on your first roll, it wont display the result, and because of the inner brackets, will just display 0 - there's no way to roll what you actually rolled. You could do  /roll [[1d12>12]]d20 and you'd be able to hover over the roll to see what it rolled - but if you do roll a 12 on that first roll, the d20 might still get less than that and would be displayed as the result. So this kind of approach is not really practical.

Thank you for your answers. I hadn't though of the rollable table. I'll give it a try.