Serious keeps every stat at 1x. No boost, no drop. That might sound safe, but you're giving up a free 10% in the stat that matters most. Nature Mints (Gen 8+) make it easy to fix. Yellow predates the nature system entirely. Transfer forward to apply natures.
Serious is a neutral nature with no stat change. For speed pokemon, use Jolly or Timid instead.
Jolly
+Speed/-Sp. Attack
Max Speed for physical attackers
Timid
+Speed/-Attack
Max Speed for special attackers
| # | Pokemon | Nature | Tier | Role | Ability | Spe |
|---|---|---|---|---|---|---|
| 1 |  Gengar GHOSTPOISON | Timid | A | Special Attacker | Levitate | 110 |
| 2 |  Starmie WATERPSYCHIC | Timid | A | Special Attacker | Natural Cure | 115 |
| 3 |  Jolteon ELECTRIC | Timid | A | Special Attacker | Voltabsorb | 130 |
| 4 |  Arcanine FIRE | Jolly | A | Physical Attacker | Intimidate | 95 |
| 5 |  Scyther BUG | Jolly | A | Physical Attacker | Technician | 105 |
| 6 |  Mew PSYCHIC | Timid | A | Bulky Support | Synchronize | 100 |
| 7 |  Ninetales FIRE | Timid | B | Special Attacker | Flashfire | 100 |
| 8 |  Zapdos ELECTRIC | Timid | B | Special Attacker | Pressure | 100 |
| 9 |  Dugtrio GROUND | Jolly | B | Physical Attacker | Arenatrap | 120 |
| 10 |  Alakazam PSYCHIC | Timid | B | Special Attacker | Magic Guard | 120 |
| 11 |  Charizard FIRE | Timid | B | Special Attacker | Blaze | 100 |
| 12 |  Tentacruel WATERPOISON | Timid | B | Bulky Support | Clearbody | 100 |
| 13 |  Moltres FIRE | Timid | B | Special Attacker | Flame Body | 90 |
| 14 |  Magneton ELECTRICSTEEL | Timid | B | Special Attacker | Magnetpull | 70 |
| 15 |  Primeape FIGHTING | Jolly | B | Physical Attacker | Defiant | 95 |
| 16 |  Electabuzz ELECTRIC | Timid | B | Utility | Vitalspirit | 105 |
| 17 |  Aerodactyl ROCK | Jolly | C | Physical Attacker | Rockhead | 130 |
| 18 |  Nidoking POISONGROUND | Timid | C | Special Attacker | Sheerforce | 85 |
| 19 |  Raichu ELECTRIC | Jolly | C | Physical Attacker | Lightningrod | 110 |
| 20 |  Ekans POISON | Jolly | C | Utility | Intimidate | 55 |
Serious is a neutral nature — no stat is increased or decreased.
Competitive Role
No competitive advantage. A stat-boosting nature is almost always preferred.
How to Get
SynchronizeLead with a Serious Pokemon that has the Synchronize ability. Wild Pokemon will match its nature. (Gen 3+)
BreedingGive the parent with Serious nature an Everstone. The offspring will inherit it. (100% since Gen 5)
Nature MintUse a Serious Mint to change stat effects to Serious. The original nature name stays but stats change. (Gen 8+)
Recommended Alternatives
What does the Serious nature do in Pokemon?
Nothing, basically. Serious doesn't change any stat. There's no boost and no penalty. Your Pokemon keeps its base stat spread exactly as-is.
Is Serious nature good?
There's no competitive reason to keep Serious. A 10% stat boost from any other nature is free power you're leaving on the table. Nature Mints (Gen 8+) let you change it without breeding.
How do I get a Serious nature Pokemon?
Catch a Pokemon and check. There's a 4% chance of any specific nature, including Serious. Synchronize ability matches the lead Pokemon's nature to wild encounters (Gen 3+). Everstone passes a parent's nature during breeding.
When should you use a neutral nature?
Almost never. The only edge case is a Pokemon that uses physical moves, special moves, and needs every defensive stat and Speed. That Pokemon doesn't really exist in competitive. Even mixed attackers prefer Naive, Hasty, or another nature that at least boosts Speed.