I have the same exact issue with my 2015 12" Macbook. I haven't done anything out of the ordinary and this just happened randomly.
I noticed the faster battery drain a few days ago, then one day the laptop stopped responding to any combination of keys (tried all
steps recommended by Apple without luck). All of the above didn't work probably due to firmware / hardware issues with the charging circuit or the battery? (there is no "chime" sound or battery low screen upon connecting to power).
I also came across someone's
recent post from iFixit detailing the same issue. My Macbook also gets warm in the logic board area when I plug it in, so maybe it's got to do with unresponsive logic board, stuck in firmware loop (with unresponsive display / keyboard)?
I wonder if this is a defect that surfaces over time (time will tell) for any 12" Macbook users. I also installed MacOS Mojave a few days ago as well - perhaps this contributes to the bricking? Would love to hear more from 12" Macbook users with Mojave installed.
[doublepost=1539064496][/doublepost]I just found out something interesting by chance. The Force Touch trackpad, if you recall, makes the clicking "noise" and "feel" artificially. This will only work if there's power delivered to the haptic feedback vibration engine below.
You can tell if the machine is "on" by trying to click on it - if it makes nose/vibrate, then the machine is technically on. Now try pressing and holding the power button while clicking the trackpad once a second until it no longer "click"s (machine powered off). You can turn it on again by pressing on the power button once gently and the "click" will reappear (machine powered on).
However, both screen and keyboard are unresponsive when the machine is "on" - hence the bricking. I'm leaning towards a stuck firmware/hardware issue - possibly with Mojave - now. I'll try to keep it "on" until it completely drains of battery for a few days and try to recharge it - hoping to do a complete power drain/cycle.