Beguiler are generating focus on deception spells hit, and most of deception spells are AoE.
So, with a level 20 cipher, when 2 enemies are in the area of (for example) Mental Binding, you are able to spam this spell over and over (if you dont miss) per env.3s .
Spamming the same spell refresh the duration (excepted if the new duration is inferior to the current one), so with a loop of some spells, it is possible to keep the effects active on the enemies, and even if their duration dont exceed the regular max duration, you can calculate quickly :
In first, a crit with Mental Binding cause 14s of Paralyse for the enemy.
then, the cipher only spam Mental Binding 9 times, with 0.3/2.8 action time. ( 9* (+3.1s) >> 27.9s of extra-duration)
or, the cipher spam also some other spell, and at a moment he have done 4 crits to the enemy with Mental Blinding and also with other spells. (4* (+7s) >> 28)
For these two situations, the total duration of the Mental Binding effect is 42 (initial 14s + 28s). But with cipher, the current effect is always between 1 and 14s however.
Cipher dont have access to Enfeebling effect, excepted while multiclassed to FF monk.
Enfeebled cause +50% of hostile effects duration, but their Total Duration . In these two case, using FF ability cause +22.5s of Paralyse (50% of 45) .
Then, recast Mental Binding do nothing (current effect is longer) excepted generate focus, and only a new Enfeebled (when the current Enf. effect is over) can cause a new 50% of total duration including the +22.5s. The tactic is simple, when the Mental Binding duration is below 14s (in this case it is my crit duration (Entropy)) and the Enfeebled effect is always running, a new spam chain refresh the duration and add to the total duration some new numbers.
Ex : there is 33s of paralyse and 40s of enfeebled when the monk hit with FF. When the monk hit with FF a new time, his cipher side had to refresh for env. 8 or 10s the Mental Binding effect. So on FF hit, this is 50% of 45+22.5+10s (+39s) added to the current paralyse effect.
With Duality of Mortal Presence, is is easy to not Enfeeble the enemy for a very long time (+10int when using cipher spells, +10con when using FF).
Draining spells self duration like Borrowed Instincts are depending of the enemy debuff duration, so with these rules.
Woedica Priest and the Writ of Mending (the only Enfeebling effect vs will) can be really potent when used after some minutes of Beguiler's spam! As PL9 spell, for most of the fight (without Brilliant) a priest have only 1 cast of that.
For Mohora/Azure Blade perspective, spamming deception spells with large AoE can be very nice.
Dispersed Suffering (Frostfall) work on the same way that Enfeebling do, but have no duration (dont need to wait the enf of the effect to reapply the +20% duration on-kill)
In the past I made some topics related to this, but without the carity for the calculation : https://forums.obsidian.net/topic/126467-class-build-the-duality-of-fractured-presence/ (but this is "extra min-maxed" and not very versatile build, but the idea is the same) and some others because I use Frostfall a lot.
I hope I was clear in my explanations, if that can help to profit better at less for FF ability.