As far as I know you have to use triggers to do it. It's frustrating because triggers cause so many problems with maps including DOTA versions that kick everyone when one person casts an ability that uses a trigger.
Here's exactly how I would do it, not saying it's the right way or the best way
*It would be easier to edit the ENDURANCE AURA ability but you could call it whatever you wanted to anyways*
- Events
______Unit - A unit owned by Player 1 (Red) Starts the effect of an ability
______Unit - A unit owned by Player 2 (Blue)..........*one for each allied player of the caster including computer players. ie - AOS spawned units*
- Conditions
______[?] (Ability being cast) Equal to *Endurance Aura *
- Actions
______Set (Triggering unit) movement speed to #####
Now, this wouldn't increase unit movement speed by a percentage rather it would set every unit's movement speed to the value you input
(#####). Not perfect but I'm sure someone can tweak this trigger and make it perfect.
I'm guessing variables might be involved and I'd also guess using variables in trigger spells might make the map less stable. Maybe I'm wrong
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Trick for making custom spells
Try editing
Rain of Chaos, this ability gives the option to run other ability for unit creation!!! Just make custom units look like whatever you want, like infernals dropping from the sky
Try playing around with this one, possibilities seem endless.
Stampede is another great one. Consider the effect of reducing the area of effect and making the units water elementals......TOB.