Your trigger leaks, and you got a lot of unneed actions. I used only half of variables you have created for making this spell work properly. Although I wasn't changing the purpose of spell I think you should change the knockback and target selection for more realistic effect and other miscellaneous stuff.
Better use expiration timers than exploding unit, trust me.
Here is your test map. I haven't removed non-used variables from variable editor, so you can see what I have done to replace them.
This indexing system is old, and inefficient - you should learn dynamic indexing/use hashtables/unit indexer. However, used that indexing to not make you confused with your own spell.
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