D&D 5E (2024) Preferences in a New Official 5.5e Specific Setting

[Yaarel]

That's the problem though. It really isn't. Other than a big bite attack, a T-Rex is a minor baddy. It can't fly, it has no magical abilities, it doesn't regenerate or breathe fire or any of the million other things it could do. Heck, it doesn't even cause fear.

So, how much CR can it actually have? An 8th level party is easily capable of dealing 100 points of damage per round. That's without expending a single resource. To make that T-Rex a credible threat, it needs at least 400 hp - enough to survive 4 rounds. A standard T-Rex has 136 Hp. Against even an 8th level party, it's unlikely to make more than one round of attacks.

IOW, to make that T-Rex a CR 13 or so creature, you need to quadruple it's hp, raise it's AC and then give it about four more attacks per round.

Tyrannosaurus Hex?

 

[Yaarel]

Really to do a decent 5e-compatible S&S game or paint S&S trappings on a Heroic Fantasy gameplay base, I would

1. Create a lot of new humaniods stat blocks
2. Create a lot of new beast stat blocks
3. Create a bunch of weapons with new weapon masteries
4. Ban a bunch of spells
5. Create a bunch of new spells
6. Design a trade-off for Prepared Spells for something else

It's less difficulty of work than volume of work. And more that you'll either create stuff no one will pay for or accidentally spawn 5 mistakes like Silvery Barbs.

It helps to focus on what themes define the setting.

Soft bans are better than hard bans.

Rather than deciding which spells dont fit a setting, focus on a list of spells that do fit the setting well. The other spells may not exist, but if they do they are peripheral, far away and-or rare. Only if a specific setting theme remains unactualized, would the DM need to invent a new spell for the focal spell list.

The same goes for backgrounds, feats, equipment, magic items. New weapon mastery properties are interesting. (There can be more techniques for using a same weapon. Dark Sun weapons are typically of obsidian and bone, and some settings have guns which I would have use Dex saving throws instead of attacks, and there might be various explosives.) Also add new fighting feats where thematic. Which species typically inhabit the setting, which classes are its fighting styles? Other species and classes might exist elsewhere but they dont comprise the day to day functioning of ordinary life.

Of course the DM can (should?) create new monsters and new magic items. Such is true for the challenges of any setting, and can effectively invite immersion in a particular setting.

Without needing to forbid the donts, focus on the dos.