Reference article
Golden seed
Golden seed adds experience to all five combat skills when consumed.
Buying and eating
Buy from the 
Seed Seller, then eat the seed in the inventory. It improves Power, Speed, Defence, Health and Special. The amount is chosen from each skill’s XP tier when the seed is eaten. A seed that crosses the level-100 threshold may produce a smaller visible level increase because XP above 10,000 uses the slower level formula.
Compared with other food
These are combat-skill seeds, rather than the energy food used in the earlier racing games.
Across the games
Compare games and editions on the 
Seed page.