We have no penalty for a captured Mond. If the Skis takes the XXI, that is not counted in any special way — the Mond is simply lost like any other card.
In Austrian and Hungarian Tarock, though, Mondfang is one of the better known penalties, and some players expect it.
How does it work under your rules: is a captured Mond penalised separately? If so, by how much, and who is credited with the points? And does the penalty apply even when it is your own partner who takes the Mond?