Because the additional redirect ability of Healing Beam replaces the original ability, the devs missed a bug where the original one doesn’t get blocked or hidden. So, if you queue up commands to use Healing Beam, it will go off as many times as you ordered it. The key is to leave a 0.5-second gap between each command to match the ability’s cooldown.
video: https://youtu.be/s7X6LcA5n48
My original reddit post: https://www.reddit.com/r/heroesofthestorm/comments/1kc891j/lt_morales_healing_beam_exploit/
There are a few other heroes with similar “issues” — like Li-Ming with her level 20 talent (she can use her ultimate endlessly), but the damage doesn’t stack. And there’s Valeera with her stealth activation. But neither of these bugs actually give any real advantage.