The strength of your pet is determined by fate and luck. All pet bonuses after each level is randomly given. Please look at the table below again.

Icon	Stat	D	C	B	A	S	Min/Max
	Str	1	1-4	1-11	1-22	1-37	5-75
	Sta	1	1-4	1-11	1-22	1-37	5-75
	Int	1	1-4	1-11	1-22	1-37	5-75
	Dex	1	1-4	1-11	1-22	1-37	5-75
	Def	4	4-13	4-44	4-88	4-148	20-300
	Atk	5	5-20	5-55	5-110	5-185	20-375
	HP	91	91-364	91-1001	91-2002	91-3367	500-6825

The Level Of The Stats... The bonuses that you recieved is determined by the max stat that you can receive in the table above. For example a D rank Tiger can only receive 1 STR. That means that it is Level 1. A "B rank Tiger" can recieve 1 to 4 STR points. Looking at the table below, that means that your bonus will come randomly from levels 1 to 3. Because the "4 STR" lies under "Level 3" and the "1 STR" lies in Level 1.

Confusing right? If you have a rank A lion, with the levels 1/3/2/6, then according to the table below, it will have 1+4+2+16 = 23 sta. So in order to have a +75 sta pet, you would need to have an S grade lion, level 1/3/5/7/9. This equals 1+4+11+22+37 = 75 sta. I hope that makes sense

	Level 1	Level 2	Level 3	Level 4	Level 5	Level 6	Level 7	Level 8	Level 9
STR	1	2	4	7	11	16	22	29	37
STA	1	2	4	7	11	16	22	29	37
DEX	1	2	4	7	11	16	22	29	37
INT	1	2	4	7	11	16	22	29	37
ATK	5	10	20	35	55	80	110	145	185
DEF	4	8	16	28	44	64	88	116	148
HP	91	182	364	637	1001	1456	2002	2639	3367

The Chances Of Each Level... As you can see from the table below, the higher rank your pet is, the lower the chances of getting a better bonus. So many people who raise a pet to "S Rank" probably didn't get the full potential of that pet.

	Level 1	Level 2	Level 3	Level 4	Level 5	Level 6	Level 7	Level 8	Level 9
D	100%	0	0	0	0	0	0	0	0
C	51%	31%	18%	0	0	0	0	0	0
B	40%	28%	18%	10%	4%	0	0	0	0
A	35%	23%	17%	12%	7%	4%	2%	0	0
S	27%	21%	17%	13%	9%	6%	4%	2%	1%

As you can see, for your Rank S pet to get the Level 9 bonus, you have a 1% chance. So even if you got your pet there, you actually have a better chance of only getting a level 1 bonus, which only gives you the lowest bonus of them all.