No there is another way - swap a matched set of key , ecu, ignition switch and shifter from a donor car
No programming is needed that way . They sell matched sets in Ebay for about $360 taken from wrecked donor cars
You must swap all 4 parts taken from the same car
That certainly works as I well know
However, that would really be my recommendation for a problem with EIS and or Shifter, Engine ECU and Key problems have cheaper alternatives that retain the Identity and Mileage of the Car
By changing the set, yes the Car will run, but then you end up with a Car that reports the wrong VIN on Diagnostic, also Post Facelift will lose the Mileage on the Cluster, and end up with either ------ or if the Donor Car has a higher mileage, you can end up with your Cluster reporting that higher mileage.
Lastly you definitely need SDS to at minimum check
the Version Codings of the used modules and then correct if necessary
, otherwise other faults can surface
If he had asked before purchasing the Key from MB, I would have recommended that he first get an Indie Locksmith to test all Keys he had, and then if proven dud, (well in this case, that one he has is definitely FUBAR), either Repair that one and / or program a new pattern Key. In UK we pay around £180 for that service with 1 new Key
BTW, to OP, since you disconnected the Battery expect things to not work correctly when you get it running, like Windows, Sunroof, Power Trunk Lifter etc etc, as these will now need Normalising, the procedures can be found in the Encyclopaedia
Disconnecting the Battery never does "reset" much, that is just "folk lore rubbish", I HARDLY EVER disconnect a Battery on Cars with this much Electronics, it causes far more grief than it is worth !!