A LotR LCG card drawing simulation with 1000 games
The percentage of games that had 4+ extra enemies was 46.8%.
The average number of rounds required was 7.2.
The average number of extra enemies was 3.4.
This simulation assumes:
Solo game
One shadow card per round, and that's the only way enemies ever get
returned to the staging area.
Enemies are never destroyed while in the staging area.
Enemies are destroyed once engaged, unless they return to the staging area.
No cards both accelerate the number of rounds AND have surge.