So here's my first pass at conversion.
Page 104:
Attack Dice: You can use the Battlesystem conversion table with 5e monsters. A 5e Monster's "THACO" is (20-its attack bonus). Instead of using a 5e monster's "Maximum Damage Per Round", use its "Average Damage Per Round". You'll have to make a judgement call on special attacks. In the conversion examples I give below, I added the 7 extra points of damage a Hobgoblin does when an enemy is nearby since, in Battlesystem, I judged there would almost always be an enemy nearby. I didn't add the extra bite attack a Gnoll can take when it drops an opponent, however, because I didn't expect every Gnoll to drop an opponent every round.
Armor Rating: To use the Armor Rating Table, convert the 5e Monster to a descending Armor Class. The 5e Monster's Armor Class is (20-5e Armor Class). So a 5e Hobgoblin, at AC 18, has a descending AC of 2, and therefor has an AR of 6. This might be too generous, since Chainmail plus Shield is only AC 4 in Second Edition (AR 7 in Battlesystem). The alternative way to do it is to simply convert the actual armor to 2nd edition and use that armor class (4 for chainmail plus shield). But you can't really do that for creatures with natural armor.
Hits Conversion Table: Instead of using the hits conversion table on page 105, just divide the 5e monster's hit points (the average given in the Monster Manuel) by 10 and round down. 5e monsters have way more hit points than in 2nd Edition, but their Battlesystem equivalents still should have more hits. That's why I propose using average damage instead of max damage to determine attack dice, and divide by 10 instead of using the chart. If the monster has fewer than 10 hit points, it has 1/2 a hit.
Morale Rating Modifiers: Use the chart as-is.
Movement: Determine the number of "inches" the monster moves by dividing its Move rate by 5. Multiply the result by 1.5. So a Hobgoblin, with a Move of 30', divided by 5 is 6, multiplied by 1.5 is 9.
Using the above system, here are the stats for a couple 5e monsters:
Hobgoblin AD 8 AR 6 Hits 1 ML 13 MOV 9
Orc AD 10 AR 8 Hits 1 ML 11 MOV 9
Gnoll AD 8 AR 7 Hits 2 ML 12 MOV 9
These aren't identical to the Battlesystem stats for these monsters but they're pretty close. If you used the 2nd Edition armor class for chainmail and Shield, the Hobgoblin stats would be identical to the Battlesystem version of the Hobgoblin, except for ML. I'm not sure if I'm calculating ML correctly since I'm not using the chart any differently than the actual Battlesystem rules use them.
completes his dungeon, state one.
