Very good! Good points, will have them fixed on version 3.1. Though I think I'm less worried about the prone/immobilized interaction, just because of the soft implications of "costs full standard movement to stand up" and "Can't voluntarily move". But I'll ponder the wording some more. You've got a sharp eye, is there anything else you think could use adjustment?
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One I just noticed today. Which I don't see anywhere on the sheet (might just be missing it since its an interaction of multiple things)
You can not become hidden if engaged. Even if invisible. (can still be engaged while hidden and remain hidden, just cant become hidden)
Additionally hidden character's do not cause engagement to others, but can still become engaged themselves. Which creates the weird state where one character has the engaged status and is hidden but the other is not hidden and also not engaged. (not sure I like this rule as in all other cases both parties becomes engaged, but I believe this is RAW)