Isen will cast Freeze the Flow of Life (ReAqCo 25), without words or gestures (he'll just use a shout or else to carry the spell into range, he just doesn't advertise his casting) succeeding (with a 1d10=7 + 44 +5 - 5 no gestures, -10 no words = 41 vs lvl 25).
Due to his opponent slow speed, Isen won't use his finesse to fast cast, so as to appear slower than he really is, in order to fool valerian and friends. Isen FC: 1d10=3 + Qik 2 = 05.
Per + Awareness: 1d10=6 + Per 1 + Aw(determining effect) 4 = 11. Not enough. So he'll just cast a random Unravelling lvl 10 spell, disregarding Animal and Imaginem: Pe 06 + Vi 04 + Sta 02 + Aura 5 + 1d10=1, 1d10=2 (again????) = 21/2 = 10, enough to dispell a lvl 20 spell.
And he casts a... 1d8=8 Vim unraveling, wrong form.
This is perfect for him, if he wins or is defeated, it is fine