[alphanumeric expression]

The goal here is to make an entity glow when a player looks at one, and only show the glow for the player looking at the entity.

new g_GlowItem[33];
//...
register_forward(FM_PlayerPreThink, "fPrethink");
register_forward(FM_AddToFullPack, "fAddToFullPack", 1);
//...
public fPrethink(id)
{
	new Index, Body;
	get_user_aiming(id, Index, Body, 320);

	if(Index)
		g_GlowItem[id] = Index;
	else
		g_GlowItem[id] = -1;

	return FMRES_IGNORED;
}

public fAddToFullPack(State, E, Ent, Host, hFlags, Player, pSet)
{
	if(!Player)
		return FMRES_IGNORED;

	if(pev_valid(g_GlowItem[Ent]))
	{
		set_es(State, ES_RenderMode, kRenderNormal);
		set_es(State, ES_RenderAmt, 25);
		set_es(State, ES_RenderColor, {0, 80, 80});
		set_es(State, ES_RenderFx, kRenderFxGlowShell);
	}
	return FMRES_IGNORED;
}

Instead of the object glowing, the player does.

I've used three different sources as references.

[Emp`]

try if( g_GlowItem[Ent] == Host ) instead of the pev_valid check

[SchlumPF*]

if(g_GlowItem[host] == Ent) and then use state not host ^^
afaik set_es has to be used with the state

[Exolent[jNr]]

Also, remove the "if( !Player )" check.

[ConnorMcLeod]

Or change it to if( Player ) if you only want to make entities glowing and not players.