Official Riftbound ruling

Does this mean that units’ Might can go to 0 or below now?

Units’ Might could always go to 0 or below; it was just really hard to actually make it happen. For example: If a Recruit was at Trifarian War Camp, it would have 2 Might (its 1 base Might, +1 from War Camp). If it got hit with Stupefy, Stupefy would “snapshot” at -1 Might, reducing the Recruit’s Might to 1. If the Recruit then moved away from Trifarian War Camp, it would lose the +1 Might bonus and end up at 0 Might. It’s much easier to make it happen with Spiritforged cards, though, so it’s worth reviewing the rules for units with 0 or less Might.

Riot's question and answer, word for word, from theRiftbound Spiritforged FAQ

The cards

  • Stupefy
    Stupefy

    Spell

    Reaction (Play any time, even before spells and abilities resolve.)

    Give a unit -1 MightMight this turn, to a minimum of 1 MightMight. Draw 1.

  • Trifarian War Camp
    Trifarian War Camp

    Battlefield

    Units here have +1 MightMight. (This includes attackers.)