Does Level 120 start with a seeded animal?

No. The first decoded frame is a clean 10x10 board with no animal and no visible X mark.

Which Level 120 cell is the red error?

r1c4 is the visible red-error square; the successful green placement is r3c4.

Finish at r1c7 in the burgundy top-right step, then the source opens the leaderboard.

Zoodoku level guide

expert 9 colors

Zoodoku Level 120 is a clean 10x10 board solved by r2c10, r7c3, r10c2, r6c6, r4c8, r8c5, r3c4, and r1c7 while avoiding red-error r1c4.

If the player asks you to sign in, open the video on YouTube instead.

Place the first animal at r2c10 in the brown right-edge singleton, fixing the far-right column.
Place the second animal at r7c3 in the light-green left pocket, using the yellow edge and brown anchor to avoid lower diagonals.
Place the third animal at r10c2 in the pink bottom band, closing the lower-left row without touching r7c3.
Place the fourth animal at r6c6 in the blue-gray bridge, preserving the central purple band for the late route.
Place the fifth animal at r4c8 in the teal right edge after the brown column has propagated its white Xs.
Place the sixth animal at r8c5 in the purple lower field, keeping the green upper-middle column open.
Place the seventh animal at r3c4 in the green upper-middle block; do not substitute red-error r1c4.
Finish at r1c7 in the burgundy top-right step and confirm the source leaderboard transition.

Colors in this level:

Green, Burgundy, Yellow, Brown, Teal, Purple, Light-green, Blue-gray, Pink

Do not tap r1c4: the source turns it into a red error X and removes one heart.
Do not finish the green family before the lower purple r8c5 placement; the source's legal green coordinate is r3c4.

Follow r2c10 -> r7c3 -> r10c2 -> r6c6 -> r4c8 -> r8c5 before the final r3c4 -> r1c7 close.
Wait for r3c4; r1c4 is the red-error top-row alternative shown in the source.

Board notes 5 details

Layout: The 10x10 opening has no seed or X mark: green spans the upper-left/middle, burgundy steps across the top-right, yellow runs down the left edge, brown is r2c10, teal fills the right edge, purple dominates the center/lower-right, light-green occupies r6c3-r7c3, blue-gray forms the row-6 bridge, and pink fills the lower-left/middle band.
Goal: Reproduce r2c10, r7c3, r10c2, r6c6, r4c8, r8c5, r3c4, and r1c7; the green placement is r3c4, not red-error r1c4, and r1c7 is last.
Opening: The first frame is clean and unseeded. The first five successful taps are r2c10, r7c3, r10c2, r6c6, and r4c8; white Xs propagate only after these actions.
Danger Zone: r1c4 becomes the source's red error during the late green sequence and costs one heart. Leave it red, place the green animal at r3c4, and finish at r1c7.
Mechanics: The yellow left edge and purple lower-right field are linked by a narrow row-6 blue-gray bridge; the final two actions return to the green upper-middle and burgundy top-right step before the leaderboard opens.

Does Level 120 start with a seeded animal?
No. The first decoded frame is a clean 10x10 board with no animal and no visible X mark.
Which Level 120 cell is the red error?
r1c4 is the visible red-error square; the successful green placement is r3c4.
What is the final Level 120 coordinate?
Finish at r1c7 in the burgundy top-right step, then the source opens the leaderboard.