Was so obsessed with these games when I was a kid that I collated all stats of all Invizimals to work out how they were calculated. At level 1 they would have 10 points assigned, according to me. For example, a starting HP stat of 100 would mean they had 1 point in HP and 9 left to assign to other stats. HP of 120 would be worth 2 points, etc. How the stats scale was based on the amount of points assigned too of course. Levelling up HP of 100 would lead to 120 -> 140 -> 160... while levelling up starting HP of 120 would lead to 144 -> 168 - > 192.

Normal invizimals would be worth 10 points. Backtracking from the level you find legendaries revealed that they were worth 12 points and dragons were worth 15. Transforming a normal into a dark would increase the base points from 10 to 16 I think. There wasn't much differentiation. No 11's. Possible a 13 or 14 exception. Changing the colour wasn't so exact because scaling wouldn't change, you just gain an extra level of recharge and if the colour was it's signature colour, an extra level of your choice.

Ha Ha Yena was one of the exceptions. Like all normals he started with 10 base points. Looking it up now he had 120 Life (2 points), 140 Stamina (3 points - crazy I can still remember this from decade ago), 5 Recharge (1 point: 5, 6, 8,...), 13 Attack (3 points: 10, 12, 13,...), 0 Armor (1 point: 0, 3, 6,...). Normals would never go above 13 attack I think. Anyway, if I recall correctly, Hyenas attack would scale normally until about 20-22 when all of a sudden it would start scaling dramatically and you could even level it when the bar was full(?) up to about a maximum of 41-44, quite a bit higher than Fire Dragon and Jungle Dragon. To compare, the FlameThrower guy would start on 13 Attack but would max out at 32. I can't recall if ge had to be the right colour to be able to reach this attack but it did mess up my point system. He was probably worth between 14 and 16 points. Not sure why this was the case and it kinda spoiled multiplayer but it was also pretty cool.

Noo I remember now. It would scale normally but at around 20-22, the next level would go to 25 but the bar wouldn't fill up. So effectively his base points have been altered and thus maximum damage has been increased causing the next upgrade to scale further.