Defeat using Pluck/Bug Bite/Payday/Thief/Knock Off/Covet - (occasionally) +1Ⓟ
Each Wealthy Tree upgrade = +20% worth. E.g. Mii's (Gold) Ⓟ reward
at end of stage starts at 10, and goes 12, 14, 16, 18, 20, 22, 24, 26,
28, and 30 with the level 10 Wealthy Tree. Small Ⓟ have a base
value of 1, as your wealthy tree levels up, they will sometimes be
worth 1 or 2, or 2 or 3 depending on your level.
These all stack, so if you have a Lucky++ Pokémon using a Ⓟ
boosting move, on an all Pokémon bonus level, you'll get maybe 5.5
coins per Pokémon defeated (excluding captures). At level 10 Wealthy
Tree that's basically 15 Ⓟ per Pokémon at a minimum, depends if
they drop any larger or gold coins.
If you keep a combo going, every 10th combo drops extra Ⓟ, and
every 50th combo seems to drop especially more coins.