Earlier this week, I reported an anomalous incident where my sneak-thief Acrobat Evangelyne failed to successfully execute her Use Magic Device (UMD) skill on a scroll 20 times in a row, in spite of her reported 25% chance of success.
That 25% seemed off to me, although I didn’t have time to investigate. Others were curious: Samius Gurubo asked “Did you do the % maths yourself or just look at the tool tip?”
I just looked at the tool tip. But today, today I am going to do the maths. Myself.
Handily, this will also serve as a good demonstration of the ways that stacking works in DDO.
Here is Evangelyne at the beginning of this exercise, hanging out with her cat Whiskers and enjoying nature in the Vale of Twilight. Note her UMD score of 18.
We have to start somewhere
A scroll of Greater Teleport has a UMD difficulty of 44. 44-18 = 26, meaning Evangelyne would have to roll a 26 on a 20-sided die to successfully UMD the scroll. An impossibility, even with DDO’s often-weighted dice.
She equips an item that increases her Charisma by five. This has a net effect on her charisma modifier of +3. Since UMD is a Charisma skill, her UMD skill increases by 3 also.
- UMD skill 21. 44-21 = 23, Evangelyne would need to roll a 23. Still not possible. 0% chance.
There are other ways to boost your Charisma, and every point of Charisma modifer also improves UMD. But Evangelyne does not have any of them. So instead, she dons a magic item: the hat “The Big Top” adds a +1 Enhancement bonus to UMD.
- UMD skill 22. 44-22 = 22, Evangelyne would need to roll a 22. Still not possible. 0% chance.
She activates the Elite Spider Cult Mask. This item adds a +1 Profane bonus to all skills, including UMD. The Profane bonus does stack with the Enhancement bonus from The Big Top.
- UMD skill 23. 44-23 = 21, Evangelyne would need to roll a 21. Still not possible.
She equips her Voice of the Master. This item provides a +1 Luck bonus to all skills and saves. Luck stacks with both Profane and Enhancement, so her UMD improves to 24.
- UMD skill 24. 44-24 = 20, Evangelyne would need to roll a 20 on a 20-sided die. At last, a possibility, even if only a meager 5% chance.
The basic rules of stacking can be summarized as (all Feat modifiers) + (best Enhancement modifier) + (best modifier from spells, effects, or equipment). There are some screwy exceptions to this, of course, this is a complex game, but in general you can assume that you will be able to stack together modifiers from Feats, Enhancements and Equipment/Spells.
But not multiple modifiers from the same source and type. Two Enhancement bonuses of the same type will not stack. Nor will multiple equipment or spell modifiers.
Evangelyne was able to stack three different modifers from the Voice of the Master, the Big Top, and the Elite Spider Mask because they are different types and the bonus type matters. Yes, they are all equipment bonuses but one is an luck bonus, one is an enhancement bonus, and the other is a profane bonus.
She equips her Ring of Persuasion. This item adds a +3 Competency bonus to all Charisma-based skills. Competency is yet another bonus type and will successfully stack with all of her other equipment.
- UMD skill 27. 44-27 = 17, Evangelyne would need to roll a 17 on a 20-sided die. Things are looking up! 20% chance.
She adds her Shield of Command. This item adds a +2 Competency bonus to all Charisma-based skills. Except, oops, we already have a Competency bonus from one of our other items. A better one. DDO selects only the highest bonus of each type, in this case the +3 from the Ring of Persuasion, and ignores the rest. Evangelyne’s Shield of Command has no effect.
- UMD skill 27. 44-27 = 17, Evangelyne would need to roll a 17 on a 20-sided die. Still at a 20% chance.
She equips her Planar Gird, which by itself has no relevant effect, but then uses it’s Greater Heroism clickie. Greater Heroism adds a +4 Morale bonus to all skills, saves and attacks. Morale is another new type, the entire +4 will count!
- UMD skill 31. 44-31 = 13, Evangelyne would need to roll a 13 on a 20-sided die. Now we really getting somewhere! 40% chance.
As one final attempt: Evangelyne uses her pumped-up UMD to cast a Scroll of Prayer. This scroll has a much lower UMD requirement, only 28, and Evangelyne can successfully cast it 120% of the time. But wait, nothing happens?
Prayer adds a +1 Luck bonus to attacks, damage, skills and saves. But we already have a Luck bonus from the Voice of the Master. Spell modifiers and Item modifiers of the same type do not stack. Prayer has no effect.
- UMD skill 31. 44-31 = 13, Evangelyne would need to roll a 13 on a 20-sided die. Still a 40% chance.
And that is her Peak UMD. There are other ways she could boost it even further although they require a visit to the trainer or to Fred the feat swapper
The feat Skill Focus: UMD would add another 3 points, and since it is a feat, would stack with everything including other feats.
The Mechanic enhancement Skill Boost adds 2-4 points of type Action Boost to all skills. Since it is an enhancement, it would stack with all feats and with the sum of item+spell modifiers, and with any other enhancements that are not also of type “Action Boost”.
Other skill enhancers will come into play when she reaches level 20: epic skills and destinies await. But for now, she is level 16 and 40% is pretty good for a high-level scroll like Greater Teleport, that’s nearly one in two, although with Evangelyne’s recent luck it would still probably take her 10 tries.
It’s also 15% better than I was able to come up with earlier this week. So there’s that.