Advice for the next level up (beguiler)

[Quentinas]

Hello to everyone, as my character is near the level up and he would gain a feat I was thinking what a good feat could be for the situations in which he is now
First the party composition
A fey ri paladin of freedom/hellbreaker that will continue the prestige class (it would be the second level of that) with a powered winter wolf as mount
A human bard 6/dirgesinger 4/spellfire wielder 1 (don't ask but probably will continue the spellfire wielder)
A feral tibbit warblade 5/bloodstorm blade 5 (he is focused on using an oversized two handed weapon and will continue the prestige class probably)
And finally my character
A True Neutral illumian beguiller 8/unseen seer 3 the sigils are vaul and krau
First thing I will not take a level of rogue (i'm the optimizer of my group so is fine if I don't add damage to what they are dealing but only support and controlling spells) I'm basically the only caster of the group with the bard that help sometimes but rarely and my feats for now are quite simple , I can think about anything that don't lose a spellcaster level even if the Krau sigil can still cover me for one
1° Subtle sigil
1° (thanks to a flaw) Darkstalker
3° Spell focus (illusion)
5° (bonus) Silent spell
6° Greater spell focus (illusion)
7° (bonus) Spell focus (enchantment) this is the level where I started the unseen seer
9° Greater spell focus (enchantment)
I have (with items) 13 of strenght , 16 of dexterity, 14 of constitution ,22 of intelligence , 12 of wisdom , 14 of charisma
The situation is that two of the followers of the paladin (i don't know if he has leadership probably as his mount his stronger and could be boosted by his feat) were taken away by a Lilitu and a fey ri wizard to a floating island where are countries that worship demons (and maybe devils) . So now we want to free them and as we don't have any means to teleport we will use or a scroll of shadow walk or a scroll of greater teleport. Our plan was to go to the nearest on the ground city and from there going on the island , but we even could use directly the scrolls to go on the island.We will not level up before going to the island so consider that we will not have shadow walk and near no means to fly except for the fey ri and eventually scrolls or potions that we can buy

I know that the next level of unseen seer or beguiler will give me nothing but that is not the problem but the feat is the problem as I don't know what could be useful. One of my ideas was to take extend spell for anti individuation on the party mage armor and something like that, or spell penetration (we could meet spell resistance that are quite high and for that I took the 8th level of beguiler) or mastery of the dream to boost the DC , but I don't know , what you would suggest? The deity of my character is Boccob for the eventual arcane disciple

[Biffoniacus_Furiou]

It's generally recommended that a Beguiler who's not good aligned take one level of Mindbender, along with the feat Mindsight. This is particularly good if you picked up Ray of Stupidity with advanced learning. This also allows you to see a given creature's type (i.e. humanoid, dragon, outsider, etc.), so if you're going up against demons/devils who can shapechange you can sniff them out easier with this.

The Raiment of the Four set's Belt of the Wide Earth in MIC allows anyone with 5th level spell slots to cast Teleport.

[ChaosStar]

How'd the Paladin Qualify for Hellbreaker? Needs Sneak Attack, Skirmish, or Sudden Strike damage. Both for the class itself and for Undo Resistance feat, which is a Prereq of the class.

[Quentinas]

Sorry wrong me , hellreaver not hellbreaker, and for mindspy ...consider that among the group I'm the most optimized and while it could be good it could be too much

[Troacctid]

I agree that Mastery of Dreams would be good, but you know what would be even better? Shadow Weave Magic. It boosts your DC for illusions and enchantments and it also boosts your spell penetration. What a deal! I'd be all over it if it were me. Then you could even take Pernicious Magic later (perhaps with a level of shadow adept to get it as a bonus feat), which is like Spell Penetration and Greater Spell Penetration combined.

Mastery of Twisted Shadow is potentially a good defensive choice. This would also be a fine level to take a bloodline feat—perhaps Celestial Bloodline, if you're expecting to face demons.

As the only caster in the party, you could also be well positioned to take Craft Wondrous Item. The beguiler spell list has enough staple crafting spells to make it work, and the paladin and bard can contribute some of the ones you're missing.

[Quentinas]

I agree that Mastery of Dreams would be good, but you know what would be even better? Shadow Weave Magic. It boosts your DC for illusions and enchantments and it also boosts your spell penetration. What a deal! I'd be all over it if it were me. Then you could even take Pernicious Magic later (perhaps with a level of shadow adept to get it as a bonus feat), which is like Spell Penetration and Greater Spell Penetration combined.

Mastery of Twisted Shadow is potentially a good defensive choice. This would also be a fine level to take a bloodline feat—perhaps Celestial Bloodline, if you're expecting to face demons.

As the only caster in the party, you could also be well positioned to take Craft Wondrous Item. The beguiler spell list has enough staple crafting spells to make it work, and the paladin and bard can contribute some of the ones you're missing.

Good advices , thanks! For the Shadow weave magic , even if there is the spellfire, is better if not as is not the forgotten realms campaign setting ,and the spellfire became like a curse that can be uncontrollable and we talk with many Mystra's (or the parallel of the wordl) so it could be a problem.
I didn't think about mastery of twisted shadow and is quite interesting, especially if I use illusions that block the vision of the enemy so I can hide for surprise casting

And for the bloodline feat...Probably I will need to talk to the DM about these , as the most obvious one (penumbra bloodline) is good , but with shadow of a conjuration (it was one of the spell I learned through advance learning) we have seen that I was making too much as I (as a player) know too much the spells of the 3.5 so the other couldn't do anything