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The wizards behaviour is set to seek out and stand on a mana well when MP is low, if a free one is found in fov, else cast magic missile on target or phase to escape if there is enough MP left and target is adjacent, and last resort to attack. The way to tackle these will be very much dependent on your current build and stash of items, and one of the possible rewards is that they have a higher chance of dropping tomes. The occurrence of Mana wells is also related to biome strength, and the tomes could appear anywhere in the game, though the chances are slimmer. Both phase and magic missile can of course be used by the player too.
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