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We have the ability to place down bombs that stay for a while after explosions. We have an ability to make bombs face a certain direction (even if it does nothing at the moment).

How about something different than bombs then?

Let's say, you charge up the item and create a fake decoy-knight and place it on the ground, all mobs around drop aggro from players and focus on this one. I'm sure some of you remember Ratchet & Clanks dummy-ratchet deployer.
It'll be tough of course, can't have it be killed by just one mob, that'd be terrible.
The upgraded version can explode and do a small amount damage to those around? Or perhaps slowly move in the direction you placed it in?
If you think this is overpowered, you should complain at the gravity bombs that cannot be killed by enemies and deal damage overtime while the enemies are stuck in it, helpless. This decoy can be destroyed when it is piled up by enemies.
It's a pretty classic thing, many games have it but it woul still be really fun to use.

Or how about turrets? We do have the Mecha Turrets.
A player can place down 1 turret, like a bomb. Upgraded turrets can turn and actually aim at mobs instead of just shoot straight ahead.
Different type of turrets do different status effects/damage type, y'know like the gunpuppies, fire, rocket and so on.
They can be destroyed by mobs and are very fragile, though.
Perhaps it can come with an armour set which increases the limit of turrets you can have up? Like up to three.
Because they'd last until destroyed by an enemy, their duration is long. Long duration means they'll do very little damage and only be useful if you use it over time, like in an arena. In a place you move around much you'll have to set it up over and over and it does too little damage to be useful there.

Or mines perhaps? I haven't tried all bombs but I don't THINK there is one that doesn't trigger until an enemy steps into its radius field. You'll have one down at a time, if you try to place a new mine when there is one that isn't triggered, the first mine will blow up and the 2nd will be the one that needs to be triggered.
This way you can be more skillful and trigger your bombs before an enemy reaches them, if it casts a status effect it'll be sure to catch them if it's a fast mob.
All our bombs trigger a few seconds right after we've placed them which makes things pretty dull and limited, very few bombs actually stand out.

Hell, even 'nades would be really fun. Smaller bombs you throw in quantities much like Seerus gigantic turret does.
You throw the grenades and if they hit a mob they blow up or if they do not, they have a small timer on them before they blow up. They're not accurate and they bounce around a bit so they would only be good when fighting a cluster of enemies, they're weaker than bombs but you don't have to approach the enemies to use 'em. Perhaps upgraded ones can be magnetized and slowly follow mobs or sticky?
I'm thinking about 3 grenades are thrown when the charge is done, each grenade does about 20% damage of a normal bomb. So it's 40% weaker than the bomb equivalent. The time it has to be charge would be as slow as your average bomb.
They'd be real weak things, the only advantage is their range so you can throw them over gaps and such.

Now I don't know how their duration, damage and statuses would be but even if I were to suggest these things, OOO would have to figure out what's balanced themselves still.
Just some vague ideas I'm sure many would think would be really fun.

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TL;DR

Decoy-knight: You place it and mobs aggro onto it until it dies. Upgraded version can walk/explodes (perhaps with a status effect).

Turrets: You place it down and it shoots in one direction with some type of ammo. Upgraded versions can be automatic and aim/home at mobs. Destroyable.

Mines: A bomb that doesn't blow up 'til a mob actually walks onto its range. Pretty boring.

Grenades: You throw a quantity of tiny bombs that bounce around 'til their timer runs out and they blow up, if they directly hit an enemy they blow up instantly. Less damage than bombs but they're ranged so with the right tactic it can be worth it. Upgraded can be sticky and not bounce around, can stick to mobs or be magnetized and slowly follow a monster.

Extra: Armour set to increase quantity of turrets/mines/decoys you can place?