Strange

Our bard stuck one up a dragons ass. “ all the way up” while it was “dead”. long story short it got possessed. Then tried to run after us. Ripping the rod out of her stomach. Easy 25 damage. (Extra 5 for creativity)

so if you had 2 immovable rods and enough upper body strength, could you climb through the air like it was a set of monkey bars?

Quote from Uuuh >>

The Players Handbook says that:

"The hand can't attack, activate magic items, or carry more than 10 pounds."

 I've had dms let me apply pressure to the trigger of a firearm with Mage Hand. It's not an attack if you don't aim just pay attention to where people's firearms are pointed a lot of holsters point the gun at your leg, you just put it where? Your waistband? You're a eunuch!

(Dm didn't like firearms and allowed me to add an additional drawback to using them as they could be set off be any spellcaster at any time)

Quote from Fireslayer999 >>

Quote from Program_Continuum >>

8,000 pounds of daggers

Which means 6526 daggers, with just under 0.625 pound to spare

 Actually, according to the PHB, 8000 daggers.

 Stack 7999 daggers on it then throw. Hammer at it to exceed the weight and rain 7999d6 on something

For those who are worried that an ancient dragon would be one-shot by your players shoving this down its throat, a blue whale baby weighs more than 8,000 pounds, so I think an ancient dragon would weigh much more than that. Maybe it could kill smaller dragons, but for the ancient ones (and other gargantuan creatures, possibly some huge ones as well) I think the rod would just deactivate and get swallowed.

I mean, just imagine being unbreakably glued to an immovable object. The enemy won’t be going anywhere. It will only be able to flail about pathetically (unless it has long range attacks / spells…)

Something about a dc30 being the equivalent of 8000 lbs is odd to me.

8000 LBS is to completely deactivate it.

DC 30 is just move it 10 feet and leave it on.

My paladin has one.  He used it to replace the handle-grip on his shield, so when he’s defending a doorway or keeping an enemy at bay, they shall not force past him.

I always thought it would be fun if someone were to cast polymorph on a big baddie turning them into a toad or something, and then placing two of these on either side, and then cancelling the spell. In theory the BBE would be crushed by the two rods, right?

All im going say is monk artificer with 2 of these as kali sticks.

Mage Hand specifies that it can't activate magic items.

Quote from DnDNewper >>

 a action is six seconds right? how far can you possably fall in 6 seconds? and even if you still take some damage from the fall,it will still be less then the hundreds of damage from one non stop fall. also lf you are a mage,you could cast haste on yourself to help with this. (and before you ask,you should be able to count as a willing creature,and you can use a object,which this is.)

 XGtE says 500ft. IRL physics says slightly more. Fall damage caps at 200ft, for 20d6.

I don’t think giant weigh 8000 pounds

It's more likely that the rod would just rip through the hull of the ship and not actually hold it in place... As for holding a creature 'down', as people are saying, that makes no sense at all. People are acting like it weighs 8000 lbs, when in actuality it can "hold up to" the weight of 8000 lbs. Key words. "Hold up to". As the rod is free from gravity when it is activated, there would be no force from the rod pushing on the creature anyways. It would be pretty easy to just wiggle from under the rod or dig a hole in the ground to be able to slip away...

They can't move because it is glued to in-between their shoulder blades. A good prank for a party member, especially one that likes to sleep face down or face up, but technically no glue needed. I guess you could use the glue to fashion some sort of guard so they can't touch the button, idk

Quote from Arcturas88 >>

For falling a Fighter with multiple attacks could activate it multiple times a round along with bonus actions. 

 Multiple attacks does not equal multiple actions. Is there some ability that let's you activate magic items in place of an attack? I feel like that'd be overpowered.

Quote from Limrasson >>

Okey, so it's immoveable, but in which inertia system? 
Because let's say you are trying your cheezy maybe not too original strategy and put this down into the gullet of an ancient dragon.
Then the dragon flies away.
I would say the rod moves away with the dragon without actually moving. Well in a way it's always moving as long as Toril is a planet. But you put it in the stomach of a dragon where is stay, but the dragon itself is moving away.

I just posted a whole comment on Sphere of Annihilation about something similar to this. I'll copy it in another comment below. 😅

tl;dr: I don't think it'd follow the reference frame of the dragon, unless it was a VERY LARGE dragon, and you were inside it. 😛

Quote from NathS >>

My comment from Sphere of Annihilation regarding inertial reference frames and magical items: 

One problem with trying to apply the laws of physics to magical things like this, is that there's no such thing as absolute position in the real universe. There's no way for something to remain stationary without reference to some other thing.

The way I like to explain it to myself is that magical effects are based on the user's limited understanding of the world. For example, when someone activates an Immovable Rod, it doesn't actually become unmoving; it maintains its position according to what the user considers to be stationary. I think most people in a medieval fantasy world don't understand the concept of inertial reference frames, and even in reality, people can know about physics, but still probably think of the ground as unmoving at a base level.

In conclusion, I think an Immovable Rod or Sphere of Annihilation would NOT move along with a vehicle, if the user is thinking of the vehicle as moving. This isn't something that most people would be able to control. On the other hand, if the user is inside of a moving thing that's sufficiently affecting their subconscious perception of their reality, it might move along with that thing.

As an example, towards the end of the first campaign of Critical Role, Vox Machina is battling cultists inside the body of a giant undead titan. The cultists use a Sphere of Annihilation with no issue, despite the titan being in constant motion. I don't think Matt or any of the players considered this at all, but that's also kind of my point.