Ok to make this fair(and easy) for all battles HP is left at a set level pre last high level attained. You shall see below:
| Level | HP |
| 10 | 30 |
| 20 | 50 |
| 30 | 80 |
| 40 | 100 |
| 50 | 120 |
| 60 | 140 |
| 70 | 160 |
| 80 | 180 |
| 90 | 200 |
| 100 | 250 |
Any level that is between the numbers will get the HP at the Lower level. Say:
a Bulbasaur at level 27 would have 50 hp but a Bulbasaur at level 31 would have 80
A Mew at level 98 would have 200 but one at level 100 would have 250
Get it? Good