@Love Seeker forgot to add lines to set the level of the dummy's abilities to match the level of the spell the hero casts. Without that, levelling up the skill will do nothing!
In general it's best not to have a separate dummy unit for each spell. Instead you can simply make one such unit and then add all the appropriate spells to it after you create it with a trigger. In this case it may be warranted if you need it to cast CR from the air, since setting a unit's fly height isn't truly instaneous (I believe).
The two fields to set to 0 are "cast point" and "cast backswing". It only needs Locust, not Invulnerable Locust is basically Invulnerable if the unit has it on it's ability list in the OE since no units or code can target, see, or find it without a direct reference or putting it in a unit group.