Make mobs apathetic up until you attack. As simple as one mod can get.
Configuration example of apathy.hjson given:
{
// This is the default behaviour for all mobs.
// You can configure multiple behaviours for any MobEntity
// The key is either null or an Identifier of a mob, the value is an array of behaviours described later
"null": [
{
// This is the type of a behaviour
// Allowed values are: do_not_follow, if_block_broken, if_item_selected
// For if_block_broken, if_item_selected you must include the maximal_reaction_distance property
// For if_block_broken you must include reaction_block property which is an Identifier of a block
// For if_item_selected you must include reaction_item which is an Identifier of an item and reaction_item_count to form ItemStack
"type": "do_not_follow"
}
],
// Zombie will be aggressive to a player, who has broken a sandstone block in radius 16.0 or shown any amount of enchanted gapples in any hand.
"minecraft:zombie": [
{
"type": "if_block_broken",
"maximal_reaction_distance": 16.0,
"reaction_block": "minecraft:sandstone"
},
{
"type": "if_item_selected",
"maximal_reaction_distance": 16.0,
"reaction_item": "minecraft:enchanted_golden_apple"
}
],
// Skeleton will be aggressive to a playes who has shown 16 zombie spawn eggs in any hand.
"minecraft:skeleton": [
{
"type": "if_item_selected",
"maximal_reaction_distance": 32.0,
"reaction_item": "minecraft:zombie_spawn_egg",
"reaction_item_count": 16
}
]
}