Why low HP is bad

The biggest misconception in the Kaizo IronMON community is that having low HP on your main Pokemon is a good thing. This paste attempts to explain why low HP is actually bad.

There are four primary threats to end a good Kaizo run: Perish Song, Destiny Bond, Counter/Mirror Coat, and everything else. From my experience, each one is about 25% likely to happen.

Pokemon with low offenses die to Perish Song much more often, which is one reason that low offenses are much worse than low HP or low defenses. You never want your other stats to be so high that they leave no room for power. The perfect Pokemon has average HP, below-average defenses, extremely high Attack or Special Attack, and good Speed.

Pokemon with low Speed die to Destiny Bond much more often, and Pokemon with good Speed never die to Destiny Bond. Thus, low Speed is also worse than low HP or low defenses.

The final two threats -- Counter/Mirror Coat and everything else -- are the reason that low HP is bad.

Counter and Mirror Coat deal damage that is independent of your defenses, and they are extremely difficult to avoid unless you are a physical Ghost type or special Dark type. If you have below average or even average HP, these moves will usually OHKO you. If you have a setup move, you can attempt to play around them, but that often introduces other major risks such as Perish Song and confusion-inducing moves. The best defense against Counter and Mirror Coat is to have high HP, because you will almost always survive a hit.

"Everything else" includes all damaging moves, as well as threats such as Endeavor and Leech Seed. While the latter two are scary, I've never lost a good Pokemon to them. They usually happen on random trainers that you can heal after. However, I've lost many Pokemon with low HP to powerful damaging moves. This is where I believe many players are confused -- they don't realize how much more likely they are to die with a suboptimal distribution of HP/defenses.

The most optimal distribution is HP = Defense + Special Defense, with the defenses being equal. Examples below (in stat values, not base stats):
- 40 HP, 20 Defense, 20 Special Defense
- 100 HP, 50 Defense, 50 Special Defense
- 340 HP, 170 Defense, 170 Special Defense

Let's take a closer look at the middle example of 100/50/50. This is a spread you might have at Level 30. Many people would prefer 70/65/65. But if your goal is overall bulk, not just physical or special bulk, you will take more damage with that spread. This can be illustrated by calculating damage from a physical attack and a special attack and then averaging the totals. For this example, we'll choose a random high-BST Pokemon with high offenses using powerful moves.

(With 100/50/50 defenses)
Pokemon: Snorlax
Level: 23
Attack: 55
Move: Earthquake (physical)
Damage: 22-26 (average 23.6% max HP)

Pokemon: Snorlax
Level: 23
Special Attack: 55
Move: Flamethrower (special)
Damage: 20-24 (average 21.8% max HP)

*****Overall average damage: 22.7% max HP

(With 70/65/65 defenses)
Pokemon: Snorlax
Level: 23
Attack: 55
Move: Earthquake (physical)
Damage: 17-20 (average 25.9% max HP)

Pokemon: Snorlax
Level: 23
Special Attack: 55
Move: Flamethrower (special)
Damage: 16-19 (average 24.5% max HP)

*****Overall average damage: 25.2% max HP

The Snorlax with high HP and low Defenses is taking 22.7% of its max HP, while the Snorlax with low HP and high Defenses is taking 25.2%. That's the difference between a 5HKO and a 4HKO. More extreme spreads will see even greater damage.

Many runners will argue that low HP is still better because heals are more efficient -- that is, items such as Energypowder and Lemonade restore a higher percentage of your HP. While this is true, it's more important to avoid healing altogether, which you do by taking as little damage as possible relative to your max HP. Healing increases the risk of seeing bad moves such as Perish Song, Leech Seed, Zap Cannon, and Dynamicpunch. Also, if the Pokemon you're facing can 2HKO you, healing doesn't help at all. My best Pokemon have beaten the game with few heals used.

Low HP also makes you more vulnerable to fixed or minimum damage moves (e.g., weak multihit moves doing 2 damage each), and it makes poison a much more threatening status condition. There are other cons to low HP, and some pros, but they are trivial in comparison to those described above.