[Scripting Question] Mach and Acrobike-help!

[Auroran]

So I've been trying to implement the Acro and Mach Bikes into a vanilla version of 17.2 Essentials. The script I'm using is quite an old one (Kudos to REI) and I've performed a little cleanup to make it compatible with v17.2, and everything seems to work fine, the animations and terrain tags all work as are supposed to (though I am using placeholder graphics at the moment for the acro bike wheelies).

My issue is that bridges are completely broken, and the character is able to walk on the edge tile of a lake (though strangely not the ocean tiles). The player cannot walk further into the water, and surfing still functions normally.

I get the following error on attempting to navigate a bridge from above or underneath:

I beleive the error lies in this line of script.

for i in [2, 1, 0]
      tile_id = data[x, y, i]
      next if tile_id && @terrain_tags[tile_id]==PBTerrain::Bridge &&
             [COLOR="Red"] $PokemonMap && $PokemonMap.bridge==0[/COLOR]
      if tile_id == nil
        return false
      # Make water tiles passable if player is surfing
      elsif PBTerrain.isPassableWater?(@terrain_tags[tile_id]) &&
         [COLOR="red"]$PokemonGlobal.surfing #&& self_event==$game_player[/COLOR]
        return true
      elsif @terrain_tags[tile_id]==PBTerrain::TallGrass &&
         $PokemonGlobal.bicycle && self_event==$game_player
        return false
      elsif @terrain_tags[tile_id]==PBTerrain::Bridge [COLOR="red"]&& $PokemonMap &&
            $PokemonMap.bridge>0[/COLOR]
        if @passages[tile_id] & bit != 0 ||
           @passages[tile_id] & 0x0f == 0x0f
          return false
        else
          return true
        end

I can see from my limited understanding and the error above that the metadata PBS file doesn't define 'bridge' so removing that condition does stop the crash from happening, however, bridges then become impassable from the top (though are passable underneath) and attempts to do the same for surfing just results in all water tiles becoming passable. Due to my lack of experience, I am unsure of what these checks are actually checking for in setting the passibility, so I could really use some help in dissecting this problem to ensure any solution keeps feature functioning as intended.

Here is my full script. I inserted it above main.

Spoiler:

################################################################################
# Mach & Acro Bike Script
# By Hansiec
# Credits required
################################################################################
# * Adds the Support for Acro Bikes and Mach Bikes!
#
# * How To Use (Acro Bike):
#    - Insert Script
#    - Edit the AcroBikeFileName Setting to what your Acro Bike Graphics would be
#    - ADD THE GRAPHICS INTO THE CHARACTERS FOLDER
#    - ADD THE ITEM "ACROBIKE" (The internal name must be ACROBIKE at the very
#       least)
#
# * How To Use (Mach Bike):
#   - ADD THE ITEM "MACHBIKE" (The internal name must be MACHBIKE at the very
#       least)
#
# * How to create Acro Bike Rails:
#   - Go into the Tileset Editor (through DEBUG mode or Essentials)
#   - Find your desired Acro Bike Rails and set their Terrain Tag to 16
#   - Go into RMXP's tileset editor and set the passages (4dir) of the rails
#     to what it would normally be to pass (EG: Rails left and right need the
#     left and right passages open but the top and bottom closed)
#
#
# * How to create Acro Bike Stepping Stones:
#   - Go into the Tileset Editor (through DEBUG mode or Essentials)
#   - Find your desired Acro Bike Stepping Stones and set their Terrain Tag to 17
#   - Go into RMXP's tileset editor and set the passages of the stepping stones
#     to impassable (the script will allow you to move on them while hopping)
#
# * How to create Mach Bike Slopes:
#   - Go into the Tileset Editor (through DEBUG mode or Essentials)
#   - Find your desired Mach Bike Slopes and set their Terrain Tag to 18
#   - Go into RMXP's tileset editor and set the passages of the slope to passable
#
#
# * Updates:
#    - Fixed Where you can turn to incorrect directions on rails
#    - Fixed Where you need to do a wheelie on an Acro Bike to access rails
#    - Fixed Where there is a few frame skips between running/biking animations
#    - Fixed When you switch from the Acro Bike to a regular Bike, that the
#       regular bike has the settings of the Acro Bike
#    - Added Rail to Rail Jumping on Acro Bikes
#    - Added Mach Bike Support
#
################################################################################

module Settings
  AcroBikeFileName = [
  "boy_run", # Player A
  "girl_run", # Player B
  "", # Player C
  "", # Player D
  "", # Player E
  "", # Player F
  ]
end


module PBTerrain
  ACROBIKE = 17
  ACROBIKEHOP = 18
  MACHBIKE = 19
end


class Game_Map
  attr_accessor :acrobike
  attr_accessor :acrobike_held
  attr_accessor :forceacro
  attr_accessor :machbike_speed
  
  alias initialize_ab initialize
  def initialize
    @acrobike = 0
    @acrobike_held = 0
    @forceacro = 0
    @machbike_speed = 0
    initialize_ab
  end
  
  def passable?(x, y, d, self_event = nil)
    return false if !valid?(x, y)
    bit = (1 << (d / 2 - 1)) & 0x0f
    for event in events.values
      if event.tile_id >= 0 and event != self_event and
         event.x == x and event.y == y and not event.through
        return false if @passages[event.tile_id] & bit != 0
        return false if @passages[event.tile_id] & 0x0f == 0x0f
        return true if @priorities[event.tile_id] == 0
      end
    end
    for i in [2, 1, 0]
      tile_id = data[x, y, i]
      next if tile_id && @terrain_tags[tile_id]==PBTerrain::Bridge &&
              $PokemonMap && $PokemonMap.bridge==0
      if tile_id == nil
        return false
      # Make water tiles passable if player is surfing
      elsif PBTerrain.isPassableWater?(@terrain_tags[tile_id]) &&
         $PokemonGlobal.surfing #&& self_event==$game_player
        return true
      elsif @terrain_tags[tile_id]==PBTerrain::TallGrass &&
         $PokemonGlobal.bicycle && self_event==$game_player
        return false
      elsif @terrain_tags[tile_id]==PBTerrain::Bridge && $PokemonMap &&
            $PokemonMap.bridge>0
        if @passages[tile_id] & bit != 0 ||
           @passages[tile_id] & 0x0f == 0x0f
          return false
        else
          return true
        end
      elsif @terrain_tags[tile_id]==PBTerrain::MACHBIKE
        return self_event==$game_player || self_event==nil
      elsif @terrain_tags[tile_id]==PBTerrain::ACROBIKE && self_event==$game_player &&
      $PokemonGlobal.acrobike && (@passages[tile_id] & bit == 0)
        return true
      elsif (@terrain_tags[tile_id]==PBTerrain::ACROBIKEHOP || @terrain_tags[tile_id]==PBTerrain::ACROBIKE) && 
        @acrobike==2 && self_event==$game_player && $PokemonGlobal.acrobike
        return true
      elsif @terrain_tags[tile_id]==PBTerrain::ACROBIKE && !$PokemonGlobal.acrobike
        return false
      elsif @terrain_tags[tile_id]==PBTerrain::ACROBIKEHOP && !$PokemonGlobal.acrobike
        return false
      elsif @passages[tile_id] & bit != 0
        return false
      elsif @passages[tile_id] & 0x0f == 0x0f
        return false
      elsif @priorities[tile_id] == 0
        return true
      end
    end
    return true
  end
  
  alias update_ab update
  def update
    @acrobike_held += 1 if !$game_player.moving?
    @acrobike_held = 0 if !Input.press?(Input::A) || !$PokemonGlobal.acrobike
    @acrobike_held = 1 if Input.press?(Input::A) && $game_player.moving? &&
                          @acrobike < 2 && @acrobike != 0
    tag = pbGetTerrainTag($game_player)
    @forceacro = 0
    @forceacro = 1 if tag == PBTerrain::ACROBIKEHOP
    @acrobike = @forceacro
    @acrobike = 1 if @acrobike_held > 0
    if acrobike_held >= Graphics.frame_rate * 2
      @acrobike = 2
    end
    
    
    if $game_player.passableEx?($game_player.x, $game_player.y,
      $game_player.direction) && $PokemonGlobal.machbike && Input.dir4 != 0
      @machbike_speed += 0.1
      @machbike_speed = 3 if @machbike_speed > 3
    else
      @machbike_speed = 0
    end
    
    ### Graphical things
    graphic = Settings::AcroBikeFileName[$PokemonGlobal.playerID]
    if FileTest.image_exist?("Graphics/Characters/" + graphic) && Input.press?(Input::A) &&
      $PokemonGlobal.acrobike
      $game_player.character_name = graphic
    elsif Input.release?(Input::A)
      Kernel.pbUpdateVehicle
    end
    if @acrobike > 1
      if !$game_player.jumping?
        Kernel.pbJumpToward(0)
        pbSEPlay("jump")
      end
    end
    update_ab
  end
  
end

class Game_Player
  alias update_ab update
  def update
    dir = @direction
    update_ab
    dir2 = @direction
    # Make it so you can't turn incorrectly on rails
    if $PokemonGlobal.acrobike && terrain_tag == PBTerrain::ACROBIKE
      if !passableEx?(x, y, @direction, false)
        @direction=dir
      end
    end

    # Do a jump onto another rail
    if !passableEx?(x, y, dir2, false) && Input.trigger?(Input::A) && $PokemonGlobal.acrobike
      dir = @direction
      if (dir2 == 2) # Down
        tag = $game_map.terrain_tag(x, y + 1, false)
        if tag == PBTerrain::ACROBIKE
          $game_player.jump(0,1)
          pbSEPlay("jump")
        end
      elsif (dir2 == 4) # Left
        tag = $game_map.terrain_tag(x - 1, y, false)
        if tag == PBTerrain::ACROBIKE
          $game_player.jump(-1,0)
          pbSEPlay("jump")
        end
      elsif (dir2 == 6) # Right
        tag = $game_map.terrain_tag(x + 1, y, false)
        if tag == PBTerrain::ACROBIKE
          $game_player.jump(1,0)
          pbSEPlay("jump")
        end
      elsif (dir2 == 8) # Up
        tag = $game_map.terrain_tag(x, y - 1, false)
        if tag == PBTerrain::ACROBIKE
          $game_player.jump(0,-1)
          pbSEPlay("jump")
        end
      end
      @direction = dir
    end
    
    #### Mach Bike
    if $PokemonGlobal.machbike
      @move_speed = 3 + $game_map.machbike_speed.floor
    end
    if $game_map.machbike_speed < 2 && terrain_tag == PBTerrain::MACHBIKE
      move_down(false)
      $game_map.machbike_speed = 0
    end
  end
end

class PokemonGlobalMetadata
  attr_accessor :acrobike
  attr_accessor :machbike
end

ItemHandlers::UseInField.add(:BICYCLE,proc{|item|
    if pbBikeCheck
     $PokemonGlobal.machbike = false
     $PokemonGlobal.acrobike = false
     if $PokemonGlobal.acrobike
       Kernel.pbDismountBike
       $PokemonGlobal.bicycle = false
     else
       Kernel.pbMountBike 
       $PokemonGlobal.bicycle = true
     end
   end
})

# Add Acro Bike Property
ItemHandlers::UseInField.add(:ACROBIKE,proc{|item|
   if pbBikeCheck
     $PokemonGlobal.machbike = false
     if $PokemonGlobal.acrobike
       Kernel.pbDismountBike
       $PokemonGlobal.acrobike = false
     else
       Kernel.pbMountBike 
       $PokemonGlobal.acrobike = true
     end
   end
})

# Add Mach Bike Property
ItemHandlers::UseInField.add(:MACHBIKE,proc{|item|
   if pbBikeCheck
     $PokemonGlobal.acrobike = false
     if $PokemonGlobal.machbike
       Kernel.pbDismountBike
       $PokemonGlobal.machbike = false
     else
       Kernel.pbMountBike 
       $PokemonGlobal.machbike = true
     end
   end
})

P.S, if you could help explain what the issue is and what a solution is doing in place, that would be really beneficial for me to learn, however, it is not entirely necessary for one :)