[MP2]

FadePlayerCamera wouldn't be needed if TextDrawFade was added, and it would need an 'inout' parameter to fade in/out.

TogglePlayerChat wouldn't be a bool parameter, as there are 3 modes (on, no outline and off).
IsPlayerChatShown should be GetPlayerChatMode, because of the reason above.

MovePlayerCamera would need lookat coordinates.

TogglePlayerHead should make the blood come out like when you decapitate peds in single-player, not just make the head disappear.

I've made some changes, with comments added to things I've changed (nothing was removed, only added/improved):

pawn Code:

native Attach3DTextLabelToObject(Text3D:id, objectid, Float:OffsetX, Float:OffsetY, Float:OffsetZ);
native TextDrawFadeInOut(Text:text, fade, time); // Fade: 0=out 1=in
native TogglePlayerInteriorEnterExits(playerid, entrance, bool:toggle); // 'entrance' would be something like ENTRANCE_AMMU, ENTRANCE_PIZZA, etc. (or perhaps coordinates with a radius like RemoveBuildingForPlayer)
native ToggleClientCommand(playerid, command[], bool:toggle); // Toggle the use of a client command, like disabling /save (some people use it to ripoff other servers). Should not work for /quit (/q)
native SetPlayerWayPoint(playerid, Float:x, Float:y, Float:z); // Set the waypoint for a player
native GetPlayerWayPoint(playerid, &Float:x, &Float:y, &Float:z); // Get the player's set waypoint (0, 0, 0 if none)
native GetVehicleParamsEx(vehicleid, &engine, &lights, &alarm, &doors, &bonnet, &boot, &objective, &feature) // Add 'feature' parameter (like the one on the packer, andromada, etc.)
native SetVehicleParamsEx(vehicleid, engine, lights, alarm, doors, bonnet, boot, objective, feature); // Add 'feature' parameter (like the one on the packer, andromada, etc.) 
native ToggleVehicleBlip(vehicleid, bool:toggle); // Toggle grey blip on radar for a vehicle
native ToggleVehicleBlips(bool:toggle); // Toggle blips for all vehicles
native TogglePlayerTearGasEffect(playerid, bool:toggle);
native ToggleTearGasEffect(bool:toggle);
native Set3DTextLabelSize(Text3D:id, Float:size);
native ShowNameTags(bool:enabled, mode); // Modes: 0 = off, 1 = names, 2 = health/armour, 3 = all
native GetLOS(Float:x, Float:y, Float:z, Float:x2, Float:y2, Float:z2); // Returns the line-of-sight distance between 2 points.
native SetPlayerCheckpoint(playerid, Float:x, Float:y, Float:z, Float:size, color); // Add color parameter
native SetPlayerRaceCheckpoint(playerid, Float:x, Float:y, Float:z, Float:size, color); // Add color parameter
native SetPlayerChatBubble(playerid, text[], color, Float:drawdistance, expiretime, LOS); // Add LOS parameter
native WalkToPos(Float:x, Float:y, Float:z, mode); // Make the NPC walk to a point. The modes are: 0 = walking, 1 = jogging, 2 = sprinting
native CreatePlayerPickup(playerid, model, type, Float:X, Float:Y, Float:Z, Virtualworld)
native ToggleVehicleCollision(vehicleid, bool:toggle);
native ToggleVehicleCollisionForPlayer(playerid, vehicleid, bool:toggle);
native ToggleObjectCollision(objectid, bool:toggle);
native TogglePlayerObjectCollision(playerid, objectid, bool:toggle);
native FadePlayerCamera(playerid, bool:fade, Float:speed); // Not necessarily needed if TextDrawFade is added (though could prevent textdraw limit being used)
native SetWaterLevel(Float:height);
native SetWaveHeight(Float:height);
native GetPlayerCursorPos(playerid, &Float:x, &Float:y);
native GetMouseClickPos(playerid, &Float:x, &Float:y); // What is this meant to do? Same as above..?
native TogglePlayerRadar(playerid, bool:toggle);
native SetPlayerChatMode(playerid, mode); // mode - 0=off 1=on 2=no outline
native GetPlayerChatMode(playerid); // Returns: 0=off 1=on 2=no outline
native SetPlayerCameraLookAtVehicle (playerid, vehicleid);
native SetPlayerCameraLookAtPlayer (playerid, lookatplayerid);
native MovePlayerCamera(playerid, Float:x, Float:y, Float:z, Float:x2, Float:y2, Float:z2, Float:speed);
native SetVehicleHandling(?);
native PutPlayerInCrane(playerid, craneid);
native TogglePlayerSPCheat(playerid, cheatname[], bool:toggle);
native GetTrainDirection(vehicleid); // Returns true if the train is driving clockwise on the train track, false if it is going counterclockwise.
native SetTrainDirection(vehicleid, bool:clockwise);
native GetTrainSpeed(vehicleid, &Float:speed);
native SetTrainSpeed(vehicleid, Float:speed);
native UsePlayerCopShootAnim(); // Needs explanation
native SetPlayerGravity(playerid, Float:gravity);
native SetVehicleGravity(vehicleid, Float:gravity);
native IsPlayerUsingJoypad(playerid);
native TogglePlayerScoreboard(playerid, bool:toggle);
native SetScoreHeader(header[]); // or something similar - changes the 'score' header to header[]
native GetPlayerNoise(playerid, &Float:noise);  // just like in the burgulary missions (callback also)
native ToggleClassSelection(bool:toggle); // Disable class selection (players spawn straight away when joining (unless scripted otherwise))
native TogglePlayerClassSelection(playerid, bool:toggle); // Same as above but for a single player
native SetPlayerID(playerid, id); // Sets the ID of a player. Returns 1 if change was successful, returns 0 if it was unable to complete the request (invalid ID or ID taken)
native GetPlayerLungCapacity(playerid, &Float:capacity);
native SetPlayerLungCapacity(playerid, Float:capacity);
native SetPlayerParamsForPlayer(playerid, forplayerid, objective, color); // basically making objectives in selected color to show above players like in SP
native SetVehicleParamsForPlayer(vehicleid, playerid, objective, color, doorslocked); // being able to choose color of the objective
native TogglePlayerHUD(playerid, component, bool:toggle); // component - 0 - Radar, 1 - Money, 2 - HealthBar, etc.
native SetPlayerGameSpeed(playerid, Float:speed); // Pretty self explanatory, toggles the slow motion effect caused by the pill pickup.
native CreateFaced3DTextLabel(text[], color, Float:x, Float:y, Float:z, Float:angle, Float:drawdistance, virtualworld, LOS);
native TextDrawMove(Text:text, Float:x, Float:y, Float:speed);
native ToggleOcuppiedVehicleDamage(bool:toggle); 
native ToggleOcuppiedVehicleDamageForVehicle(vehicleid, bool:toggle); 
native ToggleWorldSun(bool:toggle);
native AddScoreboardColumn(name[], position) // Position is the position of the column (like before player id column, after player id column, etc).
native RemoveScoreboardColumn(name[]);
native SetScoreboardColumnValue(playerid, name[], value);
native SendDeathMessageForPlayer(playerid, killer, victim, reason);
native AttachVehicleToObject(vehicleid, objectid);
native ShowPlayerDialog(playerid, dialogid, style, caption[], info[], {Float,_}:...); // Change button1[] and button2[] to allow for 1 or more buttons
native TogglePlayerMouseCursor(playerid, bool:toggle);
native TogglePlayerControllable(playerid, mode) // modes: 0 - controllable 1 - cant move player or camera (current) 2 - can't move but can move camera
native SetPlayerMaxHealth(playerid, Float:health); // If health is above 100, it will increase the healthbar size
native GetPlayerMaxHealth(playerid, &Float:health);
native TogglePlayerSpeedBlur(playerid, bool:toggle);
native ToggleSpeedBlur(bool:toggle);
native ToggleVehicleDamage(vehicleid, bool:toggle); // Works on vacant vehicles too (vacant vehicles set to invincible by default).
native ToggleCombineHarvesterDeath(bool:toggle); 
native TogglePlayerHead(playerid, bool:toggle); 
native GetPlayerPageSize(playerid);

pawn Code:

forward OnPlayerDamageObject(playerid, objectid, Float:damage, destroyed); // To detect, for example, when a player shoots an explosive barrel (object destruction could/should also be synced with other players)
forward OnPlayerEnterVehicle(playerid, vehicleid, seatid); // Add seatid parameter, and returning 0 should prevent entrance
forward OnPlayerClickPlayer(playerid, clickedplayerid, source); // Add sources: CLICK_SOURCE_CHAT and CLICK_SOURCE_NAMETAG (MP2: how would CLICK_SOURCE_CHAT work when using SendClientMessage for chat as I do in my server (to add IDs)? I'm guessing this would only work for default chat.
forward OnPlayerVend(playerid, oldmoney, newmoney, machinetype);
forward OnPlayerCasinoPlay(playerid, oldmoney, newmoney, casinoid, machinetype); // Machine type is like vending machine, blackjack, etc. casinoid is the casino (4 dragons, casigulas, redsands)
forward OnPlayerRecieveStuntBonus(playerid, amount, details[]); // 'details' contains a string of the details of the stunt, such as distance and height (like GetPlayerNetworkStats)
forward OnPlayerDeath(playerid, killerid, reason, bodypart); // Add bodypart parameter (BODYPART_HEAD, BODYPART_TORSO etc.)
forward OnPlayerMouseClick(playerid, press, buttonid); // Press would be 1 if the button was pressed, 0 if released. buttonid would be LMB, RMB, MMB, etc.
forward OnPlayerShoot(playerid, weaponid, Float:x, Float:y, Float:z); // x y z are where the bullet hits
forward OnVehicleDeath(vehicleid, reason); // Reason would be explosion or water
forward OnEnterExitModShop(playerid, enterexit, interiorid); // returning 0 here will prevent the player from entering