I want to make certain abilities have autocast turned on so that they constantly trigger whenever off cooldown/buff expires.

They are essentially passive abilities (cloak, increased attack speed, decreased damage aura) but apparently adding Stats -> e_abilEffectFlagAutoCast isn't enough.

e_acquireLevelDefensive = Autocast animation shows, never actually autocasts
e_acquireLevelNone = Autocast animation never shows
e_acquireLevelOffensive = Autocast animation shows, never actually autocasts
e_acquireLevelPassive = Autocast animation never shows

If I could duplicate the shield effect from the SFE games, I would use that, but I can't seem to find an unlocked version of the map, hence I can't figure this out at all. Apparently I have to add an instant effect to allow the ability to be autocast?

You'll need to give it an auto-cast validator, such as Is Dead.

If you want it to always happen no matter what, why not instead use a behavior with a periodic effect?

I need it to drain energy and be able to turn off. For example, cloak with 12 second duration, 11 second cooldown and increases damage by 50%, or a 10 energy cost buff that increases damage and decreases attack speed with 5 second duration, 5 second cooldown.

I'm also editing an existing map that probably wasn't the best in the world anyway, so a simple autocast modification should fix the issues we have with the current map (Night of the Dead).

Imagine I want to have a Sentry's Guardian Shield be on autocast, so it won't stop casting it until I tell it to or you run out of energy.

Alright, so have you tried adding an auto-cast validator?

Adding the validator seems to work.