[RPG] What creature of CR 5 or lower has the highest Constitution saving throw bonus

dnd-5emonster-designoptimizationzombies

What creature of CR 5 or lower has the highest Constitution saving throw bonus?

I am currently DMing a campaign and have slowly been introducing higher and higher Con save creatures as zombies, as a local necromancer tries finding the best.

Zombies' Undead Fortitude trait says:

If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Players have been having lots of fun with Zombie bear jokes at the zombie that stood back up six times.
I tried looking myself but currently don't have a lot of time to search before the session this weekend due to my work schedule changing.

Requirements

  • CR 5 or lower
  • Can't be an elemental or something that is already undead
  • Would prefer to avoid a fey due to already having done 2 zombie
    redcaps and a zombie yeth hound
  • Any published 5e books are fair game. (If you want to do an honorable
    mention from a previous edition, just state the edition so I can look
    at it and transfer it over.)

Best Answer

Barbed Devils and Otyughs (with a +7 mod to Con saves)

It's possible to use D&D Beyond to get a filtered monster list that answers this question. You can do this by selecting all monster types except fey, elemental, and undead, then filtering to CR 0-5 creatures, and filtering to monsters proficient in Con saves using the advanced filter.

Here's the final list, sorted from highest to lowest CR (since higher-CR creatures are likely to have higher modifiers). The top 4 in the list:

There are a few others with a +6 or +5 mod, but I decided to skip ahead to another tied for the highest:

I'm not seeing any others with a +7 modifier or higher for Con saves.