It's not possible without a roll20 subscription. There are two workarounds you could use: First, there's nothing special about using evens. success on 2,4,6 is exactly the same as success of 4,5,6, or exactly the same as rolling a d2 with success on 2. On a digital platform you dont have to mirror the tabletop mechanics exactly: there is no difference at all in the probabilities to do it this way. Another way would be to use a rollable table. Each item in the table, you enter a name, a weight, and a picture. For the picture, put in a die face, so you have the images of 1 2 3 4 5 and 6. For the name, put just the number 1 for pictures 2, 4, and 6; and 0 for the numbers 1, 3, and 5. for all weight = 1. Call the table d6 . Then when you roll /roll ?{Dice?|1}t[d6] you'll get the sum of the even dice, as well as the images of the dice rolled.
