Please help! Bootloop. Can't get into recovery
You just erased your boot image, 


  I think you should stick with the proper terminology. When reading from /dev/zero it simply yields an infinite amount of (ASCII) zero bytes (after all it's a character device). /dev/null when used to write to is much closer to what one could describe as a black hole. But those are two different devices with different semantics.
  ( 0xC0000022L - comment)


dev/zero is 'an infinite amount of zero bytes' in Android, DD is used for copying.  Here's what you ran in English:

Copy ( IF ) Input File = Zero Bytes ( OF ) Output File = Boot File  

You effectively flashed your boot with a series of zeros ( Erased ).  

So now that's gone, you'll need to flash it back with Fastboot..

If your device has a locked bootloader, you'll need to flash it back via SP Flash Tool.

I am working on a solution using SP Flash Tool and the stock 7.0 boot image,



Ok before anything, do a complete backup of all regions using SP Flash Tool 
MTK Backup &amp; Restore video guide


Download a stock boot.img 


You may need a full firmware to extract the boot.img
Here's the firmware i found, may be wrong moto c plus firmware on rootmygalaxy.net

Download these repair files MT6737M Files
Open SP Flash Tool version 5.16 or newer
Extract the files to a folder (Folder1) on your PC
Extract your boot.img from the firmware and place it in your folder (Folder1) 
Now you'll have four files 


MT6737M_Android_scatter.txt
Preloader_xx.bin
recovery.img ( twrp ) 
boot.img ( stock )    

Open the Scatter file in SP Flash Tool


It should automatically locate the files if no names have been changed       

Unselect Preloader 


You are only flashing boot &amp; recovery    

Select DOWNLOAD as the method of Flash  


NEVER SELECT FIRMWARE UPGRADE ETC..    

Turn Off The Device  


Make sure Quick Boot is not keeping your device switched on    

Place the USB end into your PC    
Hit start in SP Flash Tool     
Plug the other end of the USB into your device    
Wait for Flash OK    


P.S Please follow the backup guide to make sure if anything gets overwritten by an incorrect scatter file, we can restore it.

Tips :
 Each connection is a called a Handshake with the preloader, you can only use one handshake per action in SP Flash Tool, so you'll need to disconnect the usb and reconnect it to make another preloader handshake for any following action.     

Do not move your device while it's flashing, try to keep the usb cable as still as possible.