Gonna start by saying that I love that nothing dies. I do. I think it's on-point for the game's theme and it's a bold choice for a minis game. The objective is good, too. Your writing is concise and clear. You did a great job, here.
I think the game would be a lot more interesting with walls. Having a lot of open space makes it feel like an arena, and just having even 3-4 rooms, especially if they're all connected to the central room and each other, is going to deepen the tactical thinking and the usefulness of some spells.
If you're going to have a grid you have to have rules for diagonal movements. It should be noted that the biggest issue with grids is that diagonal movements allow for models to move much greater distances. This will be an especially exasperated issue in your game, because it's all about movement.
I love the big monster making things rough for players, but I can imagine situations where a player finds the Talisman early, then the monster keeps the other player at bay. Or, worse, the monster has no effect on the game at all. Your monster behavior could use some tweaking. Punishing the losing player by having the Monster go after the team without the Talisman is going to be a feels bad moment, but also leads to a less interesting game. A way to make the Monster affect things in addition to bashing would be good, too.
I think the IGO-UGO system you've got is a disservice to your design. Alternating Activations would allow for players to react to one another, would allow players to interrupt the plans of others, and presents a more fluid situation. It also decreases downtime and makes your game feel faster and more chaotic while increasing the tactical depth.
One last thing before spells. Not a huge fan of the Talisman pick-up being random. At least, not without something mitigating that randomness. I thought for sure I'd see an auto-pick-up option from the students but did not. Adding one would add a nice wrinkle into the design.
Spells: I dislike that they're once-per-game. Changing it will require some fine-tuning, of course. I think it's perfectly serviceable as is, and this is just preference, but if I'm going to play a game about wizards, I want to do wizarding.
Some spells are clearly just better than others. Without rooms to funnel pieces into specific places I think Magmatic Rift is going to be kind of pointless, for example.
I know you wanted me to go over ranges, but I just can't get a sense for that without sitting down to playtest it, and I think you've got bigger fish to fry at the moment without trying to square that away. What I said earlier stands, of course, and I really do think this could wind up being a pretty fun game.