Some things to look for include looking at the set symbols for crisp print quality, the fake will have colors bleeding into each other. Another key thing to look for is on the Official Nintendo Logo the real pack will be all white when the fake will have some yellow in the logo. The Wizards symbol on a fake pack will also be a bit off, the real pack looks crisp and properly printed with no print errors.
The Venusaur pack is a vintage repack. These packs were made in the mid 2000's buy some less then legitimate companies printing new wrappers that they photocopied thus the lower print quality. These packs have real vintage Pokémon cards in them due to it being cheaper to use the cards that were already printed then trying to make your own. Thus this strange oddity was created. These packs are often thought to be real since they were made around the same time as the originals and contain real base set cards but they have random/poor pulls due to them not being real packs and just a old repack not an authentic Base Set Pack from 1999.