Ways of adding Challenge without making custom NPCs?

[harmor]

What would you suggest?

[J3Carlisle]

wait for the npc codex

[Bearded Ben]

Add traps. Add monsters. Add more NPCs. Steal someone else's NPCs that are CR appropriate (from published adventures etc). Give the NPCs advantageous terrain (cover, height, difficult terrain). Make the PCs fight longer then they usually do.

[harmor]

J3Carlisle wrote:

wait for the npc codex

That's what sparked this post...can't wait.

[oynaz]

Improved tactics. If you are a good tactician, an intelligent group of adversaries who fight smart can be a handfull.

Or simply try putting the players in an unusual environment. On a boat, for instance.

[Chief Cook and Bottlewasher]

Add hazards - rotten floorboards (treat as trapdoors) or a slippery or tilted floor, or give the enemy an advantage. like being up on a balcony.