One of my players in a high level mythic game is optimized for stealth.

[MonkeySage]

He's a mythic level 11 arcane trickster, optimized for stealth. He legally gets +40 (minimum) on stealth checks, without going invisible.

This is a problem for me, because several of my most carefully planned encounters have been tanked by his sneak attacks.

I need to find ways to bypass such insanely high levels of stealth... And I'd prefer to do it legitimately.

(Yes, I do feel it was a mistake to run the campaign as mythic... But I feel trapped. I don't want to force my players to restat their characters because they designed these characters for a mythic campaign)

[logic_error]

Corpse candle.

[BananaNomNom]

Blindaense, unless he took dark stalker he can be seen.

[sleepyphoenixx]

He's a mythic level 11 arcane trickster, optimized for stealth. He legally gets +40 (minimum) on stealth checks, without going invisible.

This is a problem for me, because several of my most carefully planned encounters have been tanked by his sneak attacks.

I need to find ways to bypass such insanely high levels of stealth... And I'd prefer to do it legitimately.

(Yes, I do feel it was a mistake to run the campaign as mythic... But I feel trapped. I don't want to force my players to restat their characters because they designed these characters for a mythic campaign)

Optimize a monster for perception? Preferably a caster with a relevant spell like Glitterdust or Faerie Fire.
Just looking at the CR 11 bestiary shows the Thriae Seer with a native +27 perception. Replace one of her feats with Skill Focus (+6) and give her an Elixir of Vision (+10 competence for 1 hour) and you're already there. Give here a dose of Dust of Appearance and you're set.
You can optimize enemies with lesser native perception checks too, with a little more effort. Either go for the +40 to give him an equal chance or go even further if you want to negate his stealth.

And no offense, but if you neglected to account for your stealth-optimized player your encounters can't have been planned that carefully.:smalltongue:

[legomaster00156]

There are two ways to handle it. The first is having enemies capable of detecting him. The second is having ways to negate sneak attacks.
Detecting him could be done via an enemy with a particularly high Perception bonus, or one who used divination to be forewarned of an attack. Alternatively, you can look into enemies with alternative senses, such as lifesight, mindsight, blindsense/blindsight, or even just scent.
Negating sneak attack is even easier. Elementals, oozes, and a spattering of other enemies are totally immune, and the Fortification armor property negates crits and sneak attacks with a fixed % chance. Enemies can also use spells and abilities (or even just the environment) to grant themselves concealment, which automatically makes sneak attacks impossible.

[Tuvarkz]

First, content allowed?
If it's just sneak attack damage, you should maximize the monsters' HD, or throw stuff with fortification armor (or precision damage immunity), or concealment. (or a bigger DR)
Monsters wise: Tremorsense (unless he flies), Blindsight, Lifesense automatically bypass stealth in most cases.
Scent could be used by guard hounds on the alert or something, and Blindsense to a similar degree.
If you want to beat the stealth check at level 10, an half-elf cleric 10 with a familiar will have:
+10 ranks +2 racial +3 CS +6 skill focus perception +5 (eyes of the eagle)+6 (Wisdom-if not higher)+4 Alertness, which gets you to +36, about as high as you'll get short of using enemies with favored terrain/favored enemy specific to your rogue.
Issue is, there's more ways to increase stealth than to do perception, a feat to bypass blindsense/blinsight; and an easy combo with a legendary item mythic path ability to be effectively undetectable, even against what I've brought above before.
But again, this seems more of a damage issue. Which means that you should focus on dealing with his ability to deal sneak attack damage undetected.
Do not throw single opponents at your PCs anymore, they'll just get gobbled through. Action economy advantage is twice as big in Mythic games.

[GoodbyeSoberDay]

The point of mythic, at least to me, is to be able to overcome ridiculous challenges. Don't metagame his character sheet to find hard counters, or have the party "just so happen" to face encounters where there are only perception-optimized foes and blindsense monsters and the like. Just pump the difficulty of your fights straight up; add monsters, add HD, etc. Make it so they have to get the jump to have a chance in the nine hells. The only problem is if the other players aren't nearly as optimized. Then you have an intra-party balance issue that ideally would have been resolved prior to the campaign starting, and certainly isn't exclusive to mythic. In that case you might have to make bespoke encounters and metagame... but it's easier to swallow if it's made so that the other party members are designed to really kick ass, instead of designed explicitly to negate the one character.

[legomaster00156]

While I wholly agree that not every monster/encounter should be specifically designed to combat one character's shtick (the player WILL notice if they're getting particularly screwed), having enemies who are prepared for this kind of stuff isn't bad. Like all things, use it in moderation.

[Gildedragon]

Throw in some terrain difficulties: watery floors that make sneaking loud and difficult, dense fogs or mirror images that make one not see the critter as easily, likewise hidden monsters...