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However, D&D Resistances are based off of Saving Throws; Any creature can do what the game calls Taking 10, where they take their average, & add applicable bonuses. Resisting the Devourer's abilities requires a Fortitude Saving Throw of 19.
THIS IS WHY I LINKED THE IMAGE OF THE LIZARDFOLK ABILITY SCORES EARLIER, & AM RE-LINKING IT NOW.
https://cdn.**********.com/attachments/846835158480978011/927637005599379476/unknown.png
Basically, the Geckonid Subspecies of the Lizardfolk Race has premade stat ranges with defined Minimums & Maximums for Ability Scores. (Ability Scores are STR, DEX, CON, INT, WIS, CHA.)
Above 11, every two points is a range which is 1 point higher than the previous; See the chart in the Ability Scores section:
Thus, an Ability Score of 12 to 13 is +1, an Ability Score of 14 to 15 is +2, an Ability Score of 16 to 17 is +3, & so on.
Likewise for values below 10: 8 to 9 is -1, 6 to 7 is -2, 5 to 4 is -3, & 2 to 3 is -4.
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For D&D Soul Manipulation, I have to check: Priest's Spell Compendium Volume 1, Pages 69, 81, 105, 188, 309 & Priest's Spell Compendium Volume 2, Pages 309, 329, 361 & 374. Tome of Magic Page 209, twice.
From what I understand, different things to resist in D&D tend to follow the Saving Throw rules of their edition. Ex: PSCV1 & PSCV2 are for Advanced Dungeons & Dragons, AKA, 2E, so they use the rules from that edition.
According to the Advanced Dungeons & Dragons Dungeons Master's Guide:
Most monsters save as fighters, except:
1. Those with abilities of other character classes gain the benefit of
the most favorable saving throw score, i.e. be it cleric or magic-user or thief.
Includes Assassins and Monks.
2. Those with no real offensive fighting capabilities save according to
their area of ability- cleric, magic-user, thief, etc.
According to those conditions, the Adept Class likely aligns with the Magic-User, which, at Level 1, has a Saving Throw Vs. Spell of 12.... Well it means the Geckonid, considering VSBW uses rolling Take 10 plus modifiers (Which 2E doesn't have.) means the Geckonid always rolls a 10, & from the listed examples in the blogs, it would fail the save against all of them, due to being only Level 1, & thus, such Saving Throws are too difficult . (Although, if it were an Evil or Undead Cleric facing Great Circle, it could make THAT Save, but it is not, lol.)