As per comment on Penumbra Lynx need to differentiate the two.
The only cast-iron guidelines I have for Penumbra creatures so far is that they are the same creature type and have the same P/T.
So far those with abilities have color-shifted those abilities (Penumbra Elf), or mirrored them (Penumbra Owl) but that doesn't have to be set in stone as the shadow creature can be weaker than the original.

So, So far I have the following guidelines for Penumbra creatures:
1) Creature type remains the same.
2) P/T remain the same.
3) Penumbra creatures appear in every color except black, which has other penumbra effects, a-la Penumbra Essence.
4) 'Shadow' doesn't HAVE to have same/color-shifted/mirrored abilities as original, though they should be fairly close.

How is it looking?

It's looking good!

I think it's important to keep the tokens close to the original, though. It's okay to drop haste - or in fact, you could have Penumbra Lynx make a Cat with haste but not make a token for it, as per the tokens made by Goblin Assault being the same as those made by non-hasty-token-makers like Dragon Fodder.

Haste on the cat token made by Penumbra Lynx would be mostly extraneous as the Lynx is most likely to die in combat, usually attacking at which point a hasty token creature post-combat is pointless, sometimes blocking where again, haste is pointless.
Sometimes it may fall victim to spot-removal but canny players would wait until after attackers are declared to render the hasty token useless, hence why I went the way I did.