Context: I have a player who is attracted to the "flavor" of being an illusionist, but finds the School of Illusion in the PHB to be rather lackluster, especially before 14th level.
Here is an alternative. Is it balanced, relative to most of the other Arcane Schools in published sources for 5th edition?
Arcane Tradition: School of Phantasm
(Variant School of Illusion)
You practice the art of projecting your imagination out into the world with convincing apparitions, and have enhanced this ability in various respects.
Phantasmic Acumen. Beginning when you select this school at 2nd level, the gold and time you must spend to copy an Illusion spell is halved.
Multiple Minor Illusions. Beginning at 2nd level when you join this school, whenever you cast the minor illusion cantrip, its effect does not automatically end when you cast it again. Instead, you can have a number of simultaneous minor images equal to your proficiency bonus. If you already have that many active illusions, you choose which one ends upon a new casting.
Mage Hand Imagery. Beginning at 6th level, when you cast silent image while your mage hand is active, you can choose to conjoin the image to the mage hand, such that any spectral appearance of the mage hand is concealed by the image, and whatever the mage hand is carrying or manipulating appears to be carried or manipulated by the image. With an action, you can control both the image and the mage hand in a coordinated fashion.
Multi-Sensory Illusions. Beginning at 10th level, when you cast an illusion spell or cantrip, you can add a sound or an odor (or both) to it, if the spell does not already have it.
Potent Illusion. Starting at 14th level, your major image spell is so convincing that it can do damage. If the image is of a creature whose stat block includes a melee weapon attack, you can use an action to make an illusory version of that attack, using your melee spell attack bonus. On a hit, the amount of damage is one half of that shown in the stat block (rounded down) and is converted to psychic damage. There is no damage on a target that has succeeded on an ability check to see through the image, and each time a target takes damage from this feature, it attempts an Intelligence ability check to discern your illusion.