Alrighty.
Let's figure out ability scores.
Dowsizing a smilodon to Small yields...
Str 14, Dex 18, Con 10, Int 2, Wis 14, Cha 6
Dowsizing a tiger to Small yields...
Str 11, Dex 19, Con 11, Int 2, Wis 12, Cha 6
Dowsizing a lion to Small yields...
Str 11, Dex 21, Con 9, Int 2, Wis 12, Cha 6
Downsizing a leopard to Small yields...
Str 12, Dex 21, Con 13, Int 2, Wis 12, Cha 6
An already Small lynx has...
Str 7, Dex 17, Con 12, Int 2, Wis 12, Cha 7
An already Small serval has...
Str 12, Dex 17, Con 13, Int 2, Wis 12, Cha 7
Since it could supposedly take a smilodon in battle, perhaps use the downsized smilodon physical stats so it is a match when advanced to Large? We could just go with the typical lion's mental stats. Thoughts?