I must be missing something: I was under the impression that the category of the dragon detemines the amount of HP the dragon has and the amount of damage the dragon deals; and that category 9 was the highest (excluding category 10, heroics).

However, I encounter more and more dragons in the arenas that, despite having the same or worse category (and less than or equal the amount of stargs) - yet have more HP. For example:

Here I have the Blade dragon (category 9), against Dragem (category 8). Both are level 26 and both have 3 gold stars. Neither is boosted (when boosted, the HP bar is highlighted yellow). Yet the Dragem has about 30% more HP than Blade.

Why?

Higher is better for categories 1-5. Categories 6-9 are variations of category 5You can check for the exact values. dragoncityguide net -> Dragons -> Hitpoints/category

• Category 1: 3200 ATK, 8000 HP
• Category 2: 3600 ATK, 9000 HP
• Category 3: 4000 ATK, 10000 HP
• Category 4: 4800 ATK, 12000 HP
• Category 5: 5600 ATK, 14000 HP
• Category 6: 5000 ATK, 9000 HP
• Category 7: 4500 ATK, 13500 HP
• Category 8: 3000 ATK, 18000 HP
• Category 9: 6000 ATK, 13600 HP
• Category 10: 9000 ATK, 24000 HP

Category 8 has most HP but hits as a wet noodle.

yep, the category determines how much life and strength your dragon will have
for that reason, a cat-5 dragon will have a strong attack than a cat-4, even if these 2 dragons stay at level 40, with 3 gold stars.

to battles, only 4 categories are used

• cat. 8: the best defense, but weak attack.

• cat. 9: best attack, good defense (the new legendaries are inside that category)

• cat. 5: most balanced, both attack and defense is good (old legendaries, I don't see many fresh dragons inside that cat.)

• cat. 10: forget about the others one. Most brutal cat. in all the aspects. unfair and disproportionate

Thanks for the explanations. Indeed it looks like cat 5 and cat 9 are the best. Cat 6 and 7 look like some outright losers though - what would be the use for them?

6-8 are good for dragon master points which determines your ranking. Maybe somebody can confirm - the highest ranked player starts first?