Changelings, and why they're just too damn powerful

[BaneOfGiygas]

The overall problem here seems to be that the number of ways a changeling can fuck someone up is very, VERY disproportionate with what they're supposed to do. Changelings are, though I am speaking on presumptions here, supposed to be sneaky, masters of subterfuge, able to leap at lone crew members and take them down before they have a chance to scream. Why the everloving HELL, then, would you give them the complete inability to properly die and a whole motherload of abilities that they can use to mess up about three people at once? If changelings are supposed to be suited to 1v1 combat, why do they have an arsenal that could rival that of a fully decked-out nuclear operative?

In short: If you are designing a stealth-oriented antagonist type but it ends up being totally feasible and actually LIKELY for them to spend their entire round being unstealthy, acid-spitting, neuro-stinging, monkey-transforming, borderline unkillable rampagers, then there is a problem with the design.