How about something along these lines (this is assuming the ice-flinging mage manages a consequence; if not the action is easier):
"Ok, you manage to inflict the mild consequence 'Leg encased in a block of ice' on the Troll. Now it's his turn. Drawing on his supernatural recovery, the muscles in his leg bulge with renewed strength, splitting the block of ice into large chunks (supplemental action, -1 to main action). He then grabs a large chunk of ice and plays 'bowling for mages'. This counts as an Weapons maneuver (modified by Might), attempting to place the aspect 'Legs knocked out from under me' on the annoying mage that keeps trying to put blocks on him. Weapons 4, +2 for Might modifying (due to Strength), -1 for a supplemental action. Now he needs to roll his maneuver using his adjusted skill of Superb 5 against that Great 4 block in order to succeed in the maneuver (and break the block in the process)."
Now the flattened (by otherwise unhurt) caster has a choice: stay on the ground and cast his block again, or maneuver to cancel the aspect. If he does the latter, then the Troll is free to act. If he does the former, then the Troll's next action should be to tag the aspect for a grapple attempt, which would be Might (which is missing from the sample Troll in OW, but I'd rule would be at least a 3) + 2 (for Strength). This is likewise likely to succeed, with or without the block.