So... should I advance Marcellus a few seasons? He needs at least 3 seasons (perhaps 4 if experimenting doesn't work) to create the Spear of Roland in order for Kallista to recue her son from Venkath, which will also lead the dragon to undertake transformation. This meets Marcellus' bargain to Maurice as well.
In his free time during this period, he will also go and visit Simon and try to speak to Artur once in a while. His offer of friendship to both was genuine, so he will try to act accordingly.
I would go with a short story involving Marcellus in the second half of 1246. Perhaps his True Friend, Regulus Aquilius of Bjornaer, comes for a visit and asks Marcellus to join him for some tasks he cannot perform by himself?