One if the neat little rules I enjoyed in ACKS was the ability of the classes to "cleave". Down your opponent, and you get a free attack on a nearby one. If you were one of the "fighter" classes, you could cleave a number of times up to your level in a single round assuming you are able to continually down opponents. Pretty neat.
In practice it works much like the Fighter getting 1 attack per level for creatures under 1HD, but a miss ends the chain and it scales a bit with level.
There is no such rule in Crypts & Things or Swords & Wizardry, but it's an easy one to add and fits the Swords & Sorcery genre in my opinion.
I would actually treat every class in Crypts & Things, with the exception of the Magician, as if they were a Fighting class for the purpose of the cleave rule (much like all classes can backstab in C&T). Therefore, Barbarians, Fighters and Thieves would get to attempt to cleave up to one time per level per round while the Magician would be limited to a maximum of a single cleave per round.
Hopefully we get to kick the Crypts & Things campaign into motion this weekend...
Dungeons & Dragons - Players Handbook -
1 hour ago