[RPG] Is this houserule preventing effects from dropping creatures to below 1 HP if they make their save exploitable or broken

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I'm playing with the idea of adding a new house-rule to my sandbox-style game.

The rule is as follows:

If you succeed on a saving throw against an effect, that effect cannot make you drop below 1 hp.

I am hoping this will eliminate situations where an injured player rolls a 20 against a Dragon's breath weapon and then just goes down anyway because the half-damage eliminates them. In more extreme situations, it makes it so you don't instantly die with no chance if you anger a creature too powerful to defeat because the half damage might instantly kill you.

I also hope it encourages tactics both for monsters and players when dealing with a group of weaker enemies. According to the design principles, a large group of weaker creatures should remain a credible threat, but when a lightning bolt 100% takes out a whole line of them, regardless of their rolls or their cover (which is supposed to protect you from just that spell) that just isn't true anymore. With this rule, Goblins behind cover or who have advantage on the roll actually have a chance of surviving (with 1 hp, but at least they'll remain a threat). It will make these spells potent but not certain death.

However, I'd like to hear if anyone has tried this rule before, or sees any situations where this would be exploitable, broken, or "not fun".

Best Answer

This is going to be a poor idea

As other answers point out, this is going to make save-targetting spells significantly weaker, but there's also another problem you might not have thought about.

Being at 1 HP is more dangerous than being downed against big threats

This is going to leave a lot of players in combat running around with exactly 1 HP, which is prime instant-death territory. Most monsters are perfectly okay with letting a character make death saving throws to stabilize themselves, but they're not quite so okay with being stabbed in the back. (citation needed). Simply put, while downed, you are not a threat. When you're still standing at 1 HP, you're a threat and need to be taken out.

Example:

Bob the Dragon does his breath attack on Billy. Billy has a max HP of 35. The dragon deals 60 damage, but Billy succeeded on his save, so he only takes 30. That's still enough to down Billy who already took a beating from a Goblin earlier, but instead of going down, he's now at 1 HP.

That won't do, so the next turn Bob swipes at him and gets a crit. He deals 38 damage in one hit, enough to instantly kill Billy.

This will be even more obvious at lower levels, where succeeding your save against a spell might leave you standing at 1 HP next to an ogre who can one-shot kill you now even without a crit.