Route 5: found a solo Gulpin
Route 7: wild Croagunk can be found
Zubat Roost: there are solo Axew
Glittering Cave: small typo, Aurorus is the name
Route 10: Electrike hordes exist (on Y), but they seem to be the rarest encounter in the tall grass; don't know about flowers
Route 12: Heracross is exclusive to Y, not X
Coumarine City: she gives out TMforgot Acrobatics, TM92 Trick Room and TM100 Confide as well (possibly more)
Route 15: I (Y) haven't found any Mightyena, and apparently they're exclusive to X (with Liepard being the Y counterpart)
Anistar City: aside from Substitute, she also gave me TM35 Flamethrower
Route 19: found a wild Sliggoo by walking around in the swamps
EDIT:
Route 20 Guide (thanks to
SuperJOCKE for item verification)
The quickest solution to the 8th gym puzzle seems to be 2x Pink, 3x Blue, 3x Pink, 1x Yellow, 3x Green.