Ports tgstation/tgstation#39302 with adjustments, see desc of commit (#7424)

Instead of the box being 100% invisible at all times, the box will steadily become more and more visible as you move. The faster you move, the more visible the box becomes. The box will slowly become invisible again every process() cycle.
This also makes the box inherit the movement delay of it's user, meaning you're able to sprint while moving inside boxes, or walk to slow yourself down.

code/datums/action.dm

@@ -487,6 +487,27 @@
 	else
 		to_chat(owner, "<span class='cultitalic'>Your hands are full!</span>")
 
+/datum/action/item_action/agent_box
+	name = "Deploy Box"
+	desc = "Find inner peace, here, in the box."
+	check_flags = AB_CHECK_RESTRAINED | AB_CHECK_STUN | AB_CHECK_CONSCIOUS
+	background_icon_state = "bg_agent"
+	icon_icon = 'icons/mob/actions/actions_items.dmi'
+	button_icon_state = "deploy_box"
+	var/cooldown = 0
+	var/obj/structure/closet/cardboard/agent/box
+
+/datum/action/item_action/agent_box/Trigger()
+	if(!box)
+		if(cooldown < world.time - 30)
+			box = new(get_turf(owner))
+			owner.forceMove(box)
+			cooldown = world.time
+			owner.playsound_local(box, 'sound/misc/box_deploy.ogg', 50, TRUE)
+	else
+		owner.forceMove(get_turf(box))
+		owner.playsound_local(box, 'sound/misc/box_deploy.ogg', 50, TRUE)
+		QDEL_NULL(box)
 
 //Preset for spells
 /datum/action/spell_action

code/game/objects/items/implants/implant_stealth.dm

@@ -0,0 +1,38 @@
+/obj/item/implant/stealth
+	name = "S3 implant"
+	desc = "Allows you to be hidden in plain sight."
+	actions_types = list(/datum/action/item_action/agent_box)
+
+//Box Object
+
+/obj/structure/closet/cardboard/agent
+	name = "inconspicious box"
+	desc = "It's so normal that you didn't notice it before."
+	icon_state = "agentbox"
+	use_mob_movespeed = TRUE
+
+/obj/structure/closet/cardboard/agent/proc/go_invisible()
+	animate(src, , alpha = 0, time = 5)
+	START_PROCESSING(SSobj, src)
+
+/obj/structure/closet/cardboard/agent/Initialize()
+	. = ..()
+	go_invisible()
+
+
+/obj/structure/closet/cardboard/agent/open()
+	. = ..()
+	qdel(src)
+
+/obj/structure/closet/cardboard/agent/process()
+	animate(src, , alpha = alpha - 50, time = 3)
+
+/obj/structure/closet/cardboard/agent/Move()
+	. = ..()
+	if(.)
+		alpha = min(alpha + 5, 255)
+
+/obj/structure/closet/cardboard/agent/Bump(atom/movable/A)
+	. = ..()
+	if(isliving(A))
+		alpha = 255

code/game/objects/items/implants/implanter.dm

@@ -71,3 +71,7 @@
 /obj/item/implanter/emp
 	name = "implanter (EMP)"
 	imp_type = /obj/item/implant/emp
+
+/obj/item/implanter/stealth
+	name = "implanter (stealth)"
+	imp_type = /obj/item/implant/stealth

code/game/objects/structures/crates_lockers/closets/cardboardbox.dm

@@ -14,6 +14,7 @@
 	delivery_icon = "deliverybox"
 	anchorable = FALSE
 	var/move_speed_multiplier = 1
+	var/use_mob_movespeed = FALSE
 	var/move_delay = FALSE
 	var/egged = 0
 
@@ -22,7 +23,7 @@
 		return
 	move_delay = TRUE
 	if(step(src, direction))
-		addtimer(CALLBACK(src, .proc/ResetMoveDelay), CONFIG_GET(number/walk_delay) * move_speed_multiplier)
+		addtimer(CALLBACK(src, .proc/ResetMoveDelay), (use_mob_movespeed ? user.movement_delay() : CONFIG_GET(number/walk_delay)) * move_speed_multiplier)
 	else
 		ResetMoveDelay()
 

code/modules/uplink/uplink_items.dm

@@ -1293,6 +1293,12 @@ GLOBAL_LIST_INIT(uplink_items, subtypesof(/datum/uplink_item))
 	cost = 40
 	cant_discount = TRUE
 
+/datum/uplink_item/cyber_implants/stealthimplant
+	name = "Stealth Implant"
+	desc = "This one-of-a-kind implant will make you almost invisible if you play your cards right."
+	item = /obj/item/implanter/stealth
+	cost = 8
+
 // Role-specific items
 /datum/uplink_item/role_restricted
 	category = "Role-Restricted"