I agree with Carnby. I'd allow them to wear the armor as it would be part of their disguise. However, if it came down to Combat, like him, I'd also say that there would be several negatives. I'd give them the AC of Full plate, but I'd dock -2 AC for it being unacustomed to it, No Dexterity bonuses, also If any Dexterity based saving throws are needed they should be at -2, also because of it, I'd say that Attacks are also at -2 because of them being unable to move as they are accustomed too...

Mastery is all about usage. Lance and Spear may "look" similar, but they are used in fighting in totally different ways. As are Short Spear to Long Spear. 
Lances are typically used from a beast of burden (Horse or other). where a Short spear is used in melee combat and has a very active fighting style (Turning, thrusting, and even swinging), Long spears are primarily thrusting-only weapons used in circumstances where you have a "Shield Wall" (one or more characters standing in front of the long spearman, where the spearman can attack through their position to attack targets on the other side of them).

Even when you get into Swords, a lot of them are Similar, but their fighting style is specialized, and is what the master has learned...

Confused about where they got a Grenade... 

Vetus Miles wrote:

digitalelf wrote:

The AD&D 2nd Edition Green Cover, "Vikings Campaign Sourcebook" has a whole section on Rune Magic that is near 100% compatible with Hyperborea right out of the gate.
It can be purchased as a PDF on drivethrurpg and dmsguild for $9.99.

Yes, I still own that and have mined some of its material for runes. It’s a great sourcebook.

Same, I use my green books in Hyperborea as references to specific cultures all the time...
 

As others have pointed out, the Rungraver Creates the runes as a Ritual outside of combat. Then When he calls on his runes, he activates them as needed. His Runes/Day casting ability is how much energy he expends activating a Rune and how much his body can exert within a given amount of time without resting. That's the way I treat all spellcasters. Spells, whether from a God, A Book, or some other Token/Fetish, require the Energy of the caster to cast them. I break it down by spell levels, and I allow Book casters to have all their spells memorized, and pick and choose which spell is cast at the moment as it's the energy they put into the spell that is the casting, not the memorization, At least in my view. Thus if a 5th-level Wizard wanted to cast 3 extra 1st-level spells instead of his 3rd-level spell, I'd allow it. Just as if he wanted to sacrifice 3 firsts to get an additional 3rd, that would be ok also.

Vetus Miles wrote:

What are some runes you guys have added?
Looking for ideas to implement.

Here are a couple:

Rune of Ill Fortune: A rune that makes the target suffer a -1 to rolls for 10 minutes/CA of the Runcaster.
Rune of Long Striding: Grants +2 Climb/Jump/Swim checks and +5' movement speed for 10 minutes/CA of the Runecaster.
Rune of Flight: Doubles the range increment of a Weapon/Missile, ex a dagger is 5/10/15 becomes 10/20/30, or an arrow from a Comp long bow is 80/160/240 would now be 160/340/480.

From there you get the picture. Noting that Rune Casting is an art that incorporates Multiple runes and it's about how they are drawn, and the Flourishing around the rune(s) themselves.

For The Ley Lines stuff, there is a bunch of stuff out on the Kobold Press site for Mitgarrd, and it looks like it could easily be converted in for Ley Lines...

Looking pretty damn good...

ALCAVDON wrote:

There are online "converters" from 5e to OD&D back and forth. It might be worth a try.

Do you have a link? or will a google search pull one up? I've never seen any, but would be very interested...

I've seen the original, 3.5 edition, and the 5E versions kicking around. If you can't get a hold of the original, then the 3.5 would be the next easiest, 5E is a Dumpster fire...

I could see that happening. The commoners could have many alternate names for monsters/creatures/animals that add to the color of encounters.