Soulmates Puzzle system is a system in Plants vs. Zombies: All Stars, which allows the player to obtain additional puzzle pieces for already unlocked plant lines by unlocking and tiering up their soulmates.
Additional Puzzle Pieces of a specific plant line can be obtained by acquiring its fate points, with 30 fate points standing for 5 pieces, 50 fate points standing for 15 pieces and 100 fate points standing for 30 pieces. In total, the player may obtain up to 50 puzzle pieces for each unlocked plant line.
In order to obtain fate points for a specific plant line the player needs to unlock its soulmates, with each plant granting a specific amount of points - upper row grants +4/+10/+20 points, middle row grants +5/+15/+30 points and bottom row grants +8/+20/+50 points (but only when both plants are unlocked).
For example, if Diamond Spikeweed, Snapdragon, Coconut Cannon and Winter Melon are unlocked, the player will have 55 fate points for Stump line and will be able to receive 20 puzzle pieces for said line.