Tournement coming up: 600 pts, 65 model limit. The scenarios will be:
-Ill met by daybreak
-contest of champions
-domination

I have a fair chance of facing a ShadowLord, maybe more than once. Grey Company is allowed, and as everyone brings only one army each, I could be facing one. So my swamp of options includes Floi and Cirden. I thought about uber-hero combinations with Durin, Elrond, Monkey Twins or Glorfindel. With only a few days left, I've swung back toward numbers and cavalry instead.

Malbeth 75 pts
37 Warriors of Arnor 296 pts
18 Hobbit Archers 72 pts

Capt of MinasTirth mounted, lance & bow 70 pts
6 KofMT with Shield 84 pts

63 units 3 might 19 bows 597 points.

What is best for those scenarios?

You have a good solid core of troops which is a great start. Malbeth is fine to have around. Instead of the knights and the captain, I would take the monkey twins on horses (and pull of a WoA) and maybe heavy armour if you feel like dropping another warrior. That will give you a lot more needed might. I would also try and squeeze in a horn, as your army will greatly benefit from it (especially if there are ringwraiths and terror-causing models in the opponent's army).

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"War does not determine who is right, only who is left."
- Bertrand Russel

Adding a horn brings my numbers down to 51, which is too low for me. (Hobbit archers are terrific, but are not warriors, so low numbers gives me dangerously few Able Fighters).

Love those Monkey Twins. My numbers drop from a swarming 63 down to 54. What is the killing value of 2 crazed Elven Lords vs 7 mounted Knights? Would Elrond's boys kill thier points worth? The extra 4 Might points would be welcome...maybe game changing? Tough call. Opinions?

The Monkey Twins MOUNTED is the way to go! And the horn is a good suggestion for all those cowardly soldiders of Arnor. The Shadowlord will have a hard time taking down two mounted Elven lords. If on the charge, you can call a heroic combat, brake through enemy lines in one turn, kill multiple enemy soldiers, make back their points in one or two turns. Malbeth is an interesting choice, if you are struggling for points you could just swap him out for a generic Arnor Captain. Elladan and Elrohir and Malbeth though sound pretty scary!

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The Southern Fiefdoms: http://www.one-ring.co.uk/viewtopic.php?f=5&t=21928

The twins have 3 might each. So its an extra 6 might....

I did end up taking the Twins, mounted, heavy armour and bow, for a painful 180 points. They did well, one killing an Hasharin at the cost of his three might. Another fell to Glorfindel. In two matches, the Blood Bond rule rendered the other Twin useless. I could have used them better, no doubt...but I am wondering if I couldn't get more for my points. Glorfindel mounted, maybe? Or just a High Elf mounted and a swarm army of F4, D6? With these scenarios, and the armies I played against, the following list might have played well:

High Elf Captain, mounted, heavy armour, bow
Malbeth
1 Dunedain
41 Warriors of Arnor
20 Hobbit Archers

4 Might 23 Bow 64 units 597 points

While I've only played Contest of Champions a few times, every one involved only one or two kills. Surely an Elf Captain can do that? And mounted, he can avoid the Harsharins and Glorfindels...

The twins work much better if you play them well than Glorfindel on horse. Twice as much might and double stand-fast is much better. The best way to avoid blood bound is to keep them away from fights they can't win and don't let them wander off on their own little escapades unless it's capturing an objective.

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"War does not determine who is right, only who is left."
- Bertrand Russel

Yes; thanks. Keeping them together really helped. Last battle: just the twins and Aragorn--alone and on foot--managed to descimate a 42 unit Black Numenorian army--350 points--in an Ill Met by Moonlight scenario. No pesty Nazgls and limited bow range really helped, OK, but I've got new respect for the sons of Elrond.