Following the Wild Kingdom story, Marcellus will look at creating a magic item, the Spear of Roland, a dragon-slaying weapon.
He will first want to improve his score in Perdo (which is 0 at the moment). From what I see in the wiki, the best book he could study would be The Art of Destruction (L10Q15), so if it is available he would study that for 1 to 3 seasons.
The base effect would be PeAn, with the level depending on what he can achieve in the way of lab total. After 3 seasons of studying Perdo, his score would be 9.
Lab total would be Int (3) + Pe (9) + An (8) + affinity with wild beasts (8) + aura (5) + Magic Theory (5) + Inventive Genius (3) + Craft Iron (3) + Philosophiae (3) + Shape&Material Bonus (2)* = 49
Base effect could be PeAn 15 (Inflict a Heavy Wound), +1 Touch, +2 Size (for targets up to Size +7) so 30. Add in 19 levels for Penetration +38. Total level 49, so he could enchant it as a single-charge item. Subsequent spears (using the lab text) would have 10 charges (or multiple spears), should the covenant be interested in purchasing some.
Total time invested is 4 seasons.
- Marcellus could also create a more permanent item, but that would require many more seasons as well as raw vis. And the item would be vulnerable to destruction anyway.
- He could reduce the max affected Size to +4 and have the item cause an Incapacitating Wound. This might be more effective.
- He could also study Perdo for only 2 seasons and experiment. Lab total would be the same and he would save a season, provided the experiment works.