Hold Right when doing nickname, to avoid Start Buffer and not give a nickname (Not required, but I think it help)
Unless otherwise stated, always turn as late as possible. Always cut through the grass.
These paths are sorted by the frequency I encountered them when doing testing. The 3rd one listed is the one I hit (twice) in the video: https://www.youtube.com/watch?v=XhLQEwzMQ3c

NPC 1: r>R (Just before you reach him) | NPC 2: R (Block), L (Before Potion):
Enter grass before VF 1 tile early | NPC 3: U
Enter in VF at 4th tile, regular after Antidote

NPC 1: r>L (Just after you pass him) | NPC 2: R (Block), R (After Potion):
Enter grass before VF alap | NPC 3: D, U (during transition)
Enter in VF at 4th tile, regular after Antidote

NPC 1: r>D (Just after you pass him) | NPC 2: R, R (Before Potion)
Enter grass before VR 1 tile early | NPC 3: U, D
Enter alap in VF, regular after Antidote.

NPC 1: d | NPC 2: L
Enter grass before VF 1 tile early | NPC 3: U
Enter alap in VF. Go down the left side on the last stretch instead of middle.

NPC 1: d | NPC 2: L, R (After Potion)
Enter grass before VF alap | NPC 3: U, D
Enter alap in VF, regular after Antidote.

NPC 1: d | NPC 2: L, R (Before Potion)
Enter grass before VF 1 tile early | NPC 3: U, D
Enter alap in VF, regular after Antidote.
[This just got me a Rat on last tile]

NPC 1: d>D (Just before you reach him | NPC 2: L, R (Just before off screen)
Enter grass before VF alap | NPC 3: D, D
Enter in VF at 4th tile, regular after Antidote.

NPC 1: r>U (When you turn up) | NPC 2: L, R (Right after Potion)
Enter grass before VF 1 tile early | NPC 3: U, D
Enter alap in VF. On last stretch, turn left 1 tile earlier than normal.

NPC 1: u>L (Just before you reach him) | NPC 2: R (Block)
Enter grass before VF alap | NPC 3: D
Enter in VF at 7th tile. On last stretch, turn left 2 tiles earlier than normal.

NPC 1: u>U (When you turn up) | NPC 2: L, R (After Potion)
Enter grass before VF alap | NPC 3: D
Enter alap in VF, regular after Antidote.

NPC 1: r | NPC 2: L, R (Before Potion)
Enter grass before VF 1 tile early | NPC 3: U
Turn R1U1R to hug the mushroom, the enter in VF at 7th tile, regular after Antidote.

Reading this paste:
NPC 1 is the Youngster in Viridian City | NPC 2 is old man | NPC 3 is kid in the room before entering Viridian Forest
Lower case direction means facing, Upper case means move (i.e r>U means initially facing Right, moves Up)
alap means as late as possible, to still cut through the grass
4th/6th tile, means the 4th/6th tile it is possible to enter the grass, once in Viridian Forest
(Block), means the NPC blocked your path to go straight up, and must go left first
(Before/After Potion), means the NPC did it's movement before you after you picked up the Potion

Other:
You can use other NPCs, but these 3 are the ones that move, so they are the easiest to notice and keep track of.
I prioritised making the manips with the following:
1) Never waste time (No A Presses/extra steps)
2) Walk through as little grass as possible (In case you mis-indentify, still a decent chance of no encounters)
3) Turn as late as possible (Just to make them all as close as possible, and you only have to change a few movements)