In the campaign I'm playing in, our DM has set a house-rule for critical damage. So, we do
maximum damage for one set of dice, roll the second set and add modifiers at the end
instead of the typical twice-the-dice and modifiers-at-the-end rule (PHB p. 196).
Example with a L1 Guiding Bolt spell:
- regular crit = 4d6 + 4d6, average of 28
- house-rule crit = 4×6 + 4d6, average of 38
It is great when you land a crit on creature and it's fun and exciting. But, when a creature lands a crit with a special attack or spell on one of us. It can easily wipe one of us out in one blow. Let alone area-of-effect damage! It is exciting and nerve-wracking. I really enjoy it, but I am the main healer. So, I'm regularly thinking: "Who will be the next one to pop their clogs?!" On one occasion I had an inkling that the boss we were facing was going to have a final deadly move before dying - it did. There was a massive explosion of energy and anyone close to it got killed. Luckily I had run into a corner of the room in my turn and was just out of range. The whole party was wiped but muggins.
What I'm looking for is a way of thwarting critical damage against our party, if it exists.
I am not looking for the obvious! We are already working on increasing our HP pools, using temporary HPs, reducing overall damage, increasing AC/saves, and having emergency supplies, spells and scrolls. We are also working together better, more tactically, doing things like spreading out and not putting ourselves in a line where possible.
Is there a way to prevent a creature from causing critical damage on a natural 20? Or, is there a class feature or feat that prevents critical damage specifically?