Prophet teleport nerf and suddenly the game is 350% better!!!! 30s cd and putting it at cd if the tp gets canceled would be great imo. Maybe the teleport fading shadow blade invis as well...
Buffs to Tide and Enigma. Mainly the latter. I thought of midnight pulse becoming a toggle thing like Rot so he could pop it freely while channeling BLACK HOOOOOOOOOOOOOOOLE and lower the ult cd.
and of course reworking obvious stuff (bloodseeker/sniper/rikimaru/krobelus/wd etc.). I mean, Icefrog is religiously buffing heroes like bs and sniper and they still suck, at some point even a clueless beginner will realize that having a skill slot to only extend the atk range and another to (have a chance to) ministun and bonus damage is stupid.
As for items, make Vanguard being able to disassemble, buffs for Mjollnir/S&Y/Skadi I guess. I'm kinda icky with BKB, but the game would be a lot worse without it.