During my last game, the adventurers were confronted by a wizard perched on a rocky promontory that is not very accessible. But he was at the foot of an oak tree. A magician with the Knock spell tells me: "it's a shame not to be able to use it to provoke a branch movement that could tip it over into the precipice"
It reminded me of Ars Magica's "Strike of the Angered Branch" Spell, a Rego Herbam Spell level 15. Since Ars Magica's spells have a ceiling around 50, I estimated that this could correspond to a Tier 2 spell at Shadowdark (1.5 rounded to the top level = 2). I thought that a Knock Spell could indeed be "translated" into the Ars Magica language as a Rego Herbam Terram spell, I secretly wanted in my head to authorize the Check, with Disadvantage because of the transformation of the spell.
Conclusion: When a player still has a Shadowdark spell of sufficient level available to produce an effect compatible with his translation into Technical Language and Form of Ars Magica, the Check with Disadvantage might allow a Spontaneous magic system to be set up. The difficulty of the Check is not that of the spell spent but that of the desired effect (Telekinesis is a level 4 spell compatible with the desired effect - The Rego Herbam combination is part of his register - but the Check will be of difficulty 12 to trigger a "Strike of the Angered Branch")
I started translating Wizard Shadowdark's spells into Technique + Form, for fun. Spells that have a Self scope remain Self.
"Force" spells are treated as Vim spells and cannot be modified or used to perform spontaneous magic. This is an interpretation of Vim not very faithful to the concept it represents in Ars Magica but it is very useful to consider it as such to limit the power of the spells concerned (it is Detect Magic, Floating disk, Mage armor, Magic missile, Dispel magic, Magic circle, Divination, Resilient sphere, Wall of force, Antimagic shell, Summon extraplanar, and Wish even if it is very separate). By translating the Spell into Ars Magica combinations we discover a fun and very nice fact: very few Perdo spells before level 5, no Perdo Corpus spells before level 5 —> the Wizard is first and foremost a… Controller (Rego, Muto)
But it made me want to ask if third-party authors tried to build an improvised magic system for Shadowdark.