There are some challenges you must overcome to build Monte Carlo simulations in Anaplan.
Anaplan does not include a pseudo-random number generator. You either have to implement your own using Anaplan formulas and functions, or import a file of data generated by an external psuedo-random number generator. From that point, you want to generate values at random from a probability distribution. You will need to implement the probability distributions using Anaplan formulas and functions.