Greetings Hivemind of AD!
Im looking for useful Trinkets for, how could it be otherwise, Roleplay.
What i am talking about are Trinkets that for example place a visual or object on the ground or put a special effect like flames on you.
It should be a “On Use” Trinket so I/we can use it WHEN we need it.
(Wowhead link welcome)
With that said, fire away please to enlighten me and everyone else who might be interested in that Topic
One of my favorites
Makes your character grow slightly in size and then it slams the ground four or five times
Good for rage-y characters for combat
Here are some of the top of my head
-Mogu rune of paralysis
-Umbral moonglaives
-High powered flashlight
-Smoldering titanguard
-Terminus signaling beacon
-Shado-Pan dragon gun
Unfortunately, I rarely write on the forum so I can’t post links, but I hope this helps! 
Boy do I got the thing for you!
It is a simple invisibility but it is for everyone not using a stealth class.
The amount of times where I have had to sneak past my guildies to prevent ruining immersion because my char wasn’t in place for the situation is enough to run out of toes and fingers to count on.
A few I’ve used or been meaning to use:
Summons a pretty big tentacle, useful for void-y stuff.
Same effect of an Elune Stone, on a longer cooldown but still good in case you forgot to stock up.
This one doesn’t place an object but after a few stacks you can easily get, you turn into a dragonkin, which can be handy for handling costumes.
Summons a pretty big voidcaller for 10 minutes, useful for a little bit of pretend-warlock rp or some other purpose you can find. Has a big cooldown unfortunately.
I am an infamous trinket-roleplayer and gladly share what I have. Though mind, these are for shadows priests / void users (the characters I play).
I want to share something i know too
Places a Blue rune under you, useful for any sorts of magic or traps you might have triggered
I have used these quite often in my RP
Skull of guldan, drops from Illidan in BT. Gives a fel empowered aura for a short While.
Perfectly perserved cake from nighthold. Places down a cake, great for When warlocks want to show of their mage skills.
Horn of cenarius, Emerald nightmare. Sends a whisp at a friendly target. Great for When you want to do a healing spell on a non healer
This trinket makes your character do attack animation with your weapon. It´s from Tyr´s Hand questline, which can be picked without completing any other quests in Light´s Hope Chapel.
Incredibly gnomish trinket for all my Gs out there
(Makes you release sparks from your back for 10 seconds.)
I’ve yet to get my hands on it myself due to the seemingly abysmal low drop rates, but there’s a trinket from De Other Side that makes a splash of blood erupt around your character, followed by some blood-shield.
I imagine you could just immediately /cancelaura the shield part with a macro, if you just wanted the initial blood-splash effect to RP some injury. Obviously also nifty for some more sinister necromancer characters.
You can get the same blood splatter effect a lot easier with mecha bytes from Mechagon.
Creates a red rune for 1 minute with a 1 minute CD
https://i.imgur.com/eHcyhvP.jpg
Here’s a few of my favorite picks:
https://www.wowhead.com/item=72899/varothens-brooch - Zippety zap goes red lightning in RP PVP.
https://www.wowhead.com/item=31337/orb-of-the-blackwhelp - Back when I was thinking about dragon RP, this lil’ whelp transformation was neat.
https://www.wowhead.com/item=159749/hawlis-hot-spicy-chili - Safely self-combust on demand.
EDIT: Also only trinkets oops, but there’s one!
Blast down a bolt of lightning on your location.
Very cool.
I know it’s been said already, but I second the Shado-pan dragon gun. Nice flamethrower effect.
I found another one that might be useful
A Small bump so people will see it again
Evening Argent Dawn
This Time i found a Trinket for our engineers. it does needs a target though