Always put two or more casters in the test map so it's easier to test MUI stuff.
Learn tooltip has lots of typos/bad grammar. For example "untill" -> "until" , "ammount" -> "amount" , "inscreases" -> "increases".
I also prefer the standard Blizzard way of displaying ability level data.
The dummy doesn't need invulnerability ability, it has locust.
Generally if you use something more than once, save it to a variable and use the variable. Like angle from point a to point b and triggering unit. This increases performance.
Split Fireball Move should be initially off. And turned on/off when needed.
Here again, set picked unit to a variable, and use the variable instead of picked unit.
Leak:
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(Number of units in (Units within 50.00 of FireMovePoint matching...
Leak:
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Unit - Create 1 Fireball for (Owner of (Picked unit)) at (FireMovePoint offset by 53.00...
FireLoad, FireSpacing and FireHits should be loaded to a variable.
Fireball Death is unnecessary. Remove the unit from the group in the looping trigger, after you kill it.
The whole if/then/else structure could be better organized. You shouldn't have clear hashtable and kill unit twice there.