The people knocked down by Icy Terrain can, after standing up, charge or use ranged attacks against anyone within range.
I do like Icy Terrain but unlike, say, Maze of Mirrors, you can't just fire it off and know you've done something awesome.
AP should not be used to fey step... AP grasping shadows.
Since this is all hypothetical there's no right nor wrong; a strategy like "leading with color spray" can be great or bad depending on the situation.
When slowed the creatures speed is 2, it can only end it's move 1 square away from it's starting position.
Mythra's low AC is ok, because Mythra has a higher than normal HP and surge count, thanks to that pumped up constitution.
Leading with Color Spray is a sound risk, the rewards are great.
I still say since this is all hypothetical there's no right or wrong or good or bad - it's situational, and you have to pick what you think works best for the situation. If you still disagree that's fine, but I know I've personally seen color spray be "great" without a wizard's AC coming into play, so you can't really categorically exclude it or say a wizard's AC is too low to use it based on one hypothetical situation.It can be "ok", or "bad". It's rare that it would be "great"
Your hypothetical situation where all the enemies charge straight at the wizard is actually the best possible time to use shield; think how many attacks you're using the bonus +4 to! Also, encounter powers are there to be used; no need to be stingy. Since most battles last less than 5 rounds, if you can use 2 or 3 encounter powers in one turn, you're probably making a huge difference. That may be more of a personal philosophy than a general rule but it has worked well in my experience.And yes, he could use his Shield spell to get his AC up that high for that round. But, he's using up a lot of resources in round one, just for the chance to do some damage (the Daze does little) that he could probably do just as well from the back ranks.
The control aspect of a Wizard should hamper the foes, not hamper the action choices of his teammates.
Great? Dazing a few foes?
Sorry, but leading with your chin is not the way to box.
But, he's using up a lot of resources in round one, just for the chance to do some damage (the Daze does little) that he could probably do just as well from the back ranks.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.