While at first it doesn't seem an efficient trap given the fact that animated armor will need to spend part of its time establishing control. It does have a nasty aspect that the PC will be inside forcing the rest of the party to come up with a innovated way of stopping the armor without hurting (much) or killing the character inside.
Should the Animated Armor's control over the PC be implemented via the
grapple mechanic? Is that technically feasible? If so, I feel like
either the PC should get disadvantage or the Armor should get
advantage. Is there a significant difference statistically in the
outcome depending on which one of those I choose?
Basically yes, at its core should involve a contest between the two opponent's strength so the grapple use of the strength based skill Athletics is a good choice. However I would rule that can't use Acrobatics once the PC is inside the armor. Only Athletic checks are allowed.
The same with the escape attempt, once inside the only way to regain control is with a Athletic (Str) check.
If the grapple mechanic is used to implement this tactic, would it be
unfair to grant the Armor the "Damage Transfer" property of the Rug of
Smothering? I feel like attacks directed at the armor should also harm
the wearer, but effectively granting the armor complete damage
resistance (allowing it to only take half damage from virtually all
attacks) seems pretty brutal.
The Damage Transfer ability of the Rug of Smothering means that it takes longer to kill the creature. The target inside the Rug will take the same amount of damage needed to kill the Rug itself.
Now that I think about it the Damage Transfer ability was probably granted to the Rug in order to prolong the danger from the Rug's Smother attack. In light of this my recommendation is that for the Animated Armor trap, damage be equally allocated between armor and the character inside. However remember the character inside doesn't have the poison or psychic immunity the armor has.
While the Armor is controlling a PC, should the "combined creature"
(combination of PC and Armor) attack using the PC's attributes and
attacks or the Armor's attributes and attacks? For example, take a
fighter who wields a Pike who has been taken over by a suit of
Animated Armor. Can the Armor make attacks with the Pike using the
fighter's Strength, or is the Armor forever fated to only be able to
use it's default Slam attack with its own Strength score?
No that doesn't make logical sense. The way you describe it the Animated Armor is acting like an sci-fi exoskeleton with a will of its own.
Similar to #3, should the combined creature use the PC's AC or the
Armor's AC? For example, assume a fighter wielding a shield and a Ring
of Protection +1 straps on the Animated Armor and loses his grapple
check, his total AC would be 21 (base 18 from Full Plate Mail, +2 from
the shield, +1 from the Ring of Protection). Should attacks against
the PC+Armor be targeted against an AC of 18 (for just the Armor) or
21 (for the PC)?
Basically yes except that the character inside would not get a dex bonus to their AC or use of their shield.. If they still have a higher AC, I would rule that the only the Armor suffers damage if the attack is equal to or greater than the Animated Armor AC but less than the PC dex-less AC. If the PC had a shield it would be used by the Animated Armor making it a AC 20 but not the PC.
Final Thoughts
I would rule it like this
- The PC puts on the Armor
- The armor comes to life initiates a grapple check.
- If the PC succeeds, he yells help and we go back to step 2. The PC will get his normal turn.
- If the PC fails, he goes oh crap and still yells help, and now has the restrained condition similar to the result of the Rug of Smothering's smother attack.
- The armor uses it interaction to pick up the PC's weapon. If the PC has a shield then it will spend its action to pick up both weapon and shield. The armor then moves and does it action (if has one)
- PC can attempt an escape with Athletics only.
- The armor can takes it turns as long as the PC doesn't succeed on an Athletic check. The PC does then the Armor will return to fighting for control.
- If the PC makes a number of successful Athletics, your call, then he has managed to rip the armor. If the party aids him then he makes the check with advantage. I recommend at least two in a roll, no more than four in a row.
Give them a few options, with the last one being "or do something else."
Your players are a group of people with other stuff they're thinking about who are simultaneously socializing with each other as players and trying to play a game. They don't have the story and setting in their heads like you do, so you're doing them a favor by exposing your view of their goals and approaches to them.
When I GM, I find it effective to periodically say things like "So it sounds like your plan is to either do X or do Y," or "At this point you could do A, do B, do C, or do something else." Think of your campaign as a choose-your-own-adventure game where there's always an "other" option that's picked half of the time.
You can also simply reiterate their goals and their situation: "So. You know that you need to find the Foo. You're currently in a Blah room and there are two doors you haven't explored." Since you have hesitant players, you can just pick one who hasn't contributed in a while and say, "Sue. What are you doing?"
When the players are hesitant, the GM can always describe the situation, list the immediate options (leaving an "other" option to avoid railroading!), and pick someone to put on the spot. In the worst case, another player will come to their rescue and perform an action to get the plot moving.
Best Answer
Make traps that aren't about being hidden, but are about avoiding them.
The latest dungeon I ran included a trap. All along a hallway, there were massive, purple crystal structures growing from the floor to the ceiling. They were immediately obvious to anyone who wasn't literally blind. There were no rolls required, and there was no time searching for the trap because it was obvious.
The trap, however, was that they were triggered by sound. If the characters spoke too loudly or did anything that made noise, they would explode and deal damage to the players, potentially triggering a chain reaction that could easily kill them.
This turned the characters away from having to do Perception checks every five feet, and instead made it interactive and a roleplay opportunity. How were they going to communicate? How were they going to get the plate wearing orc across? What was even on the other side, was it worth it at all?
All in all, it took them 20 minutes of planning, but rather than it being 20 minutes of "I roll Perception, what do I see?" it was 20 minutes of them chatting in character and planning their course of action, and they loved it. They got to flex their roleplay muscles rather than roll dice, and they got to plan something more clever than "I roll to disarm the trap".
Make it a time investment.
But perhaps you really like hidden traps, and you think you have a particularly good one that you don't want to get rid of. No problem. A character who is constantly searching for traps is going to be wasting a lot of time. This is time that could be better spent hunting down an enemy, exploring the rest of the dungeon, completing their quests, or even resting. They can't do any of those things while they are constantly scouring every square of a dungeon for traps. So, introduce something that puts a time constraint on them.
Perhaps they know their target will be leaving soon, and wasting hours searching for traps means their target escapes.
Maybe a spell is going to cause the entrance to the dungeon to shut in three hours, sealing them in to starve to death, and they need to be quick.
It could even be something as simple as the person who gave them the quest is very picky about time, and won't be in town to pay them for completing their quest if they take longer than a few hours.
If you don't want to do something so strict, you can still punish extreme amounts of time spent searching for traps. Enemies perhaps will know they are outside the door, and the longer they spend searching, the more reinforcements that arrive or the better position they are in to ambush the players as they enter. Maybe enemies have time to sneak up and surprise the players as they waste an hour with their eyes to the floor looking for traps that aren't there.
If you are concerned about the out of game time being spent...
Perhaps your problem is not with the time being wasted in game, but rather out of game. If so, that's easily fixed: just have them roll one Perception check per room or section, rather than every hall and every door.