[RPG] How to make an encounter actually match its CR level


I recently started using encounter generators and tables. I've noticed that there are encounters like "8 Cave Spiders" or similar. While the number of enemies will result in an encounter that "should" be challenging, each creature's turn is limited to a 1v1 encounter with a player. Because of this, the player's statistics tend to make combat futile for creatures under a certain level (can only hit and save on natural 20s, can only affect players with spells or dodge players attacks on their natural 1s).

Now, is there a way to take creatures that fall into that category of 5%ers (1 in 20 chance to do anything) and make them do something useful more than 5% of the time under RAW?

I'm not asking how to modify the encounters to produce creatures that aren't 5%ers. I'm asking how to take those encounters as written and make them as challenging as they're supposed to be.

Best Answer

The ways to make monsters more challenging is to use 'player' tactics such as flanking, ambush and aid another.

Using giant spiders as an example.

Round 1 Check for surprise vs stealth (with a +14 for the modifier 11 as the base and 3 for distance). Assuming spiders get surprised, nail the PCs with eight touch attacks with web (at +5 to hit).

Round 2 PCs must get out of entanglement or take the penalties (an entangled creature moves at half speed, cannot run or charge, and takes a –2 penalty on all attack rolls and a –4 penalty to dexterity. An entangled character who attempts to cast a spell must make a concentration check (DC 15 + spell level) or lose the spell). Meanwhile spiders go after the lightly armoured types to get flanking. A couple stay back to web anyone getting loose.

Round 3 If spiders are still having problems hitting (and it is not just bad dice) they start tag-teaming with aid another to up higher.

At this point or sooner, depending on how tough your PCs are, the spiders are hitting with a +8 and starting to poison the lower STR PCs while the martial types are still getting hit with entangling every round.

An interesting read for low CR, high threat concept is http://www.tuckerskobolds.com/.