To mask the layer named as 'Lines' with the layer named as 'Mask'.

1. Select frame 12 on layer named as 'Yellow Object'

2. Choose Edit > Copy as shown in the image given below,

3. Insert a new layer (Choose Insert > Layer) above the layer named as 'Lines'

4. Rename the layer as 'Mask'

5. Insert a Blank Keyframe (Choose Insert > Blank Keyframe) at frame 13 of the layer named as 'Mask'

6. Choose Edit > Paste in Place as shown in the image given below,

7. Select the layer named as 'Mask'

8. Choose Modify > Layer

9. In the Layer Properties panel select Type = Mask and Lock = on as shown in the image given below,

10. Select the layer named as 'Lines'

11. Choose Modify > Layer

12. In the Layer Properties panel select Type = Masked and Lock = on as shown in the image given below,

13. Select frame 354 on all the layer and choose Insert > Frame as shown in the image given below,

1. Insert a new layer (Choose Insert > Layer) above the layer named as 'Mask'

2. Rename the layer as 'Image 1'

3. Insert a Blank Keyframe (Choose Insert > Blank Keyframe) at frame 11 of the layer named as 'Image 1'

4. Import (Choose File > Import) image1.png file from the images folder and convert it into a Movie Clip (choose Insert> Convert to Symbol) with the top-left Registration point selected and name it as 'image 1'

5. Choose Window > Info

6. In the Info panel, keeping top-left Registration point selected, set x position = - 12 px and y position= - 28 px.

7. Select frame 25 on layer named as 'Image 1'

8. Choose Insert > Keyframe

9. Select the 'image1' Movie Clip at frame 11 on layer named as 'Image 1'

10. Choose Window > Properties

11. In the Properties panel, set Color Style = Advance and set the Advance Color Settings as R)+=255, G)+=255, B)+=255 and Alpha = 0%. Refer the image given below,

12. Select frame 15 on layer named as 'Image 1'

13. Choose Window > Properties

14. In the Properties panel, set Tween = Motion and Ease = 100.

15. Insert keyframe (choose Insert > Keyframe) at frame 78 and frame 83 on layer named as 'Image 1'

16. Select the 'image1' Movie Clip at frame 83 on layer named as 'Image 1'

17. Choose Window > Properties

18. In the Properties panel, set Color Style = Advance and set the Advance Color Settings as R)+=255, G)+=255 and B)+=255.

19. Select frame 80 on layer named as 'Image 1'

20. Choose Window > Properties

21. In the Properties panel, set Tween = Motion and Ease = 100.

22. Select frame 84 on layer named as 'Image 1'

23. Choose Insert > Blank Keyframe

1. Insert a new layer (Choose Insert > Layer) above the layer named as 'Image 1'

2. Rename the layer as 'Image 2'

3. Insert a Blank Keyframe (Choose Insert > Blank Keyframe) at frame 83 of the layer named as 'Image 2'

4. Import (Choose File > Import) image2.png file from the images folder and convert it into a Movie Clip (choose Insert> Convert to Symbol) with the top-left Registration point selected and name it as 'image 2'

5. Choose Window > Info

6. In the Info panel, keeping top-left Registration point selected, set x position = - 12 px and y position= - 28 px.

7. Select frame 97 on layer named as 'Image 2'

8. Choose Insert > Keyframe

9. Select the 'image2' Movie Clip at frame 83 on layer named as 'Image 2'

10. Choose Window > Properties

11. In the Properties panel, set Color Style = Advance and set the Advance Color Settings as R)+=255, G)+=255 and B)+=255. Refer the image given below,

12. Select frame 90 on layer named as 'Image 2'

13. Choose Window > Properties

14. In the Properties panel, set Tween = Motion and Ease = 100.

15. Insert keyframe (choose Insert > Keyframe) at frame 249 and frame 254 on layer named as 'Image 2'

16. Select the 'image2' Movie Clip at frame 254 on layer named as 'Image 2'

17. Choose Window > Properties

18. In the Properties panel, set Color Style = Advance and set the Advance Color Settings as R)+=255, G)+=255 and B)+=255.

19. Select frame 250 on layer named as 'Image 2'

20. Choose Window > Properties

21. In the Properties panel, set Tween = Motion and Ease = 100.

22. Select frame 255 on layer named as 'Image 2'

23. Choose Insert > Blank Keyframe