Flashing stock firmware is pretty easy and simple using SP FlashTool. The tool works specifically for MTK (Mediatek) device.
Download the files below and follow the later instructions to learn how to use SP Flashtool to flash stock ROMs on supported devices.
HOW TO FLASH WITH SP FLASHTOOL
Download and install drivers for your device. If you can’t find your device driver, us this guide to download and install the driver.
Download Sp Flashtool and the your phone’s firmware package. (Firmware list)
Extract Sp FlashTool and your firmware package to different folders.
Open SP FlashTool folder and launch SP Flashtool.exe as Administrator.
Click on Scatter-loading, browse and select scatter file from the folder you extracted the downloaded firmware. (e.g, MT6582_Android_scatter.txt)
Click on Download and connect the device to PC via USB cable. Device must be turned off, before attaching to pc.
Once the device is connected to PC, a progress bar will start loading. Wait for it to complete. A green circle with Ok should popup to indicate completion.
Disconnect the device and perform a factory reset before you power on fully. Done.
If you still have questions, please ask in comments. Need your device stock firmware? request in comments too.