Add overlay video and animated text (textbox and shadow) with FFmpeg
You only have two inputs, so 2:v can't exist. Instead, you'll need a base canvas to draw the text upon. I've used the color source filter for that. And you probably want that canvas to be the same size as the video. I've used scale2ref for that. 

ffmpeg -i input -i overlayvideo \
-filter_complex \
"[0:v] setpts=PTS-STARTPTS [v01]; \
[1:v] setpts=PTS-STARTPTS [gradient]; \
color=black@0:duration=8,format=yuva444p[txtbase];[txtbase][v01]scale2ref[txtbase][v01];[txtbase] drawtext=fontfile=...font.ttf: text='Test': fontcolor=white:fontsize=54: shadowcolor=black@0.6:shadowx=4:shadowy=2: \
box=1: boxcolor=a60000@0.4:boxborderw=10:x='310':y='350',fade=t=in:st=1:d=1:alpha=1,fade=t=out:st=7:d=1:alpha=1[txt]; \
[v01][gradient] overlay [v02]; \
[v02][txt] overlay[outv]" \
-c:v libx264 -profile:v main -level:v 3.1 -pix_fmt yuv420p -c:a aac -map [outv] \
-f mp4 -y 'output.mp4'