Animating a polygon mask and cloning people: Fusion in Resolve for beginners 

How do polygon masks work, in a basic fashion in Fusion for Davinci Resolve?
Let's make a silly example and use it as a tutorial!
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You can find me also in Instagram:
/ rogerinfinland
My audio setup:
t.Bone EM800 bit.ly/2GYrhSy
Zoom F2 bit.ly/3L8YDKS
Zoom F2 bt bit.ly/3v4G1pL
Rode VideoMicro bit.ly/2RN94JR
Rode NTG4+ bit.ly/3Eqf2Y8
Zoom H5 bit.ly/2REIDGd
Zoom H1n bit.ly/2ZHSkZ2
Rode Wirless Go bit.ly/2Xl0PuP
Rode Lavalier Go bit.ly/2RPO4SJ
Mic stand bit.ly/32nhUUa
My cameras and accessories:
Sony a6400
Cage bit.ly/385auIN
L-bracket bit.ly/3b0uJJC
Cold shoe relocate bit.ly/3rK9WQm
Panasonic G9
Cage bit.ly/2Mpe4VM
L-bracket bit.ly/3pMchZn
Sony ZV-1
L-bracket bit.ly/2XkLVES
Z-cam E2c
Cage bit.ly/3rN2KmD
Assets and music from:
www.freesfx.co.uk
www.productioncrate.com/
triunestore.com/
artlist.io/
www.soundjay.com/
Software I use:
Davinci Resolve (free): www.blackmagicdesign.com/fi/p...
HitFilm Express: fxhome.com/express