Ok, after reading your description of your world situation and the hordes of undead roaming the city and your request for some Aberrations I have come up with the following possible situation.
Arri-Vastril Cult
When the material plane was weakened and the negative energy plane portal was opened and the positive energy plane was cut off the barriers between all planes was momentarily blurred. In this moment an Arri-Vastril polyp was drawn through to the city, following the scent of undeath.
Once in the city the polyp established it’s nest in an old temple of Pelor and started to draw in the local population with its Alien beauty and telepathic messages of hope. It called it’s self the Arri-Vastril Savior.
The Savior has a large radiant aura that keeps the undead at bay, and also has the effect of nourishing anyone who stays within the aura for an hour. Word quickly spread that a new ‘God’ had come to aid the worthy.
With its congregation of worshipers established the Savior was able to start to slowly reproduce and hunt the undead in order to feed.
What plans does the Alien intelligence have towards the city and its new followers? What will it be able to achieve once it has fed from a sufficient quantity of undead? What will the intelligent udead do to try and stop the cult? What will the PCs do when they discover an organisation that can effectively combat the undead but is from beyond the stars?
Only you can decide.
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I will leave the descriptions of what these creatures look like to you.
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Arri-Vastril Drone Level 2 Minion
Small Aberrant Beast XP 31
Initiative +3 Senses Perception +2
HP 1; a missed attack never damages a minion.
AC 16; Fortitude 15, Reflex 14, Will 15
Resist 10 radiant; Vulnerable 5 thunder
Speed 8
[FONT=D&D 4e icons]M[/FONT] Glowing Slam (Standard; at-will) ♦ radiant
Attack +7 vs. AC; 4 radiant damage
[FONT=D&D 4e icons]R[/FONT] Beam of Light (Standard; at-will) ♦ radiant
Range 5; attack +5 vs. Reflex; 3 radiant damage
Flickering Flash (Immediate Reaction) ♦ teleport
When Drone is missed by a melee attack it may immediately teleport 3 squares
Alignment Evil Languages arri-psy
Skills perception +7
Str 16 (+4) Dex 14 (+3) Wis 12 (+2)
Con 10 (+1) Int 12 (+2) Cha 16 (+4)
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Arri-Vastril Defender Level 4 Soldier
Medium Aberrant Beast XP 175
Initiative +4 Senses Perception +4
Cleansing Light (radiant) aura 1; all enemies starting entering or starting
their turn inside aura take 2 radiant damage
HP 54; Bloodied 27
AC 20; Fortitude 17, Reflex 16, Will 17
Resist 10 radiant, 5 psychic; Vulnerable 5 thunder
Speed 6
[FONT=D&D 4e icons]M[/FONT] Mind Slap (Standard; at-will) ♦ psychic
Attack +9 vs. Will; 1d6+4 psychic damage
[FONT=D&D 4e icons]m[/FONT] Clawed Tendril (Standard; at-will) ♦ radiant
Reach 2; attack +11 vs. AC; 1d10+4 radiant damage; on hit target is
marked until the start of Defenders next turn
[FONT=D&D 4e icons]c[/FONT] Beautiful Glow (Standard; encounter) ♦ radiant
Burst 5; attack +8 vs. Reflex; 1d6+4 radiant damage; on hit target is
immobilised (save ends)
Psychic Feedback (Immediate Reaction)
If Defender is hit by any attack with the Psychic keyword it creates
feedback with the attacker; attacker takes half the damage dealt and
both Defender and Attacker are Stunned until the end of their next turns
Alignment Evil Languages common, arri-psy
Str 18 (+6) Dex 14 (+4) Wis 14 (+4)
Con 14 (+4) Int 12 (+3) Cha 18 (+6)
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Arri-Vastril Juggernaught Level 6 Brute
Large Aberrant Beast XP 250
Initiative +4 Senses Perception +4
HP 86; Bloodied 43
AC 18; Fortitude 19, Reflex 16, Will 18
Resist 10 radiant, 5 psychic; Vulnerable 5 thunder
Speed 5
[FONT=D&D 4e icons]M[/FONT] Glowing Tentacle Slam (Standard; at-will) ♦ radiant
Reach 2; attack +9 vs. AC; 2d6+4 damage
[FONT=D&D 4e icons]m[/FONT] Double Tentacle Slam (Standard; recharge [FONT=D&D 4e icons]456[/FONT]) ♦ radiant
2 attacks; reach 2; attack +8 vs. AC; 1d10+4 radiant damage; on hit
target is pushed 2 squares
[FONT=D&D 4e icons]m[/FONT] Juggernaught Stomp (Standard; encounter)
Juggernaught moves up to 5 squares and may move through opponents
squares (it must end in a clear space); enemies it moves through in this
way may make an opportunity attack with a -2 penalty; Juggernaught
makes an attack against each creature it tramples; attack +7 vs. Reflex;
1d8+4 damage; on hit target slides 1 square and is knocked prone
You Wont Like Me When I'm Angry (Immediate Reaction)
When bloodied Juggernaught Stomp reacharges and is activated as an
immediate free attack
Alignment Evil Languages arri-psy
Skills endurance +11, athletics +12
Str 19 (+7) Dex 12 (+4) Wis 12 (+4)
Con 16 (+6) Int 10 (+3) Cha 16 (+6)
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The next creature is the Arri-Vastril Savior, the cult leader and a serious threat.
Bear in mind that the Savior has a large group of devout and grateful followers in attendance at any time, due to its large aura.
The Savior is a multi part Solo, When the Savior is reduced to bloodied it transforms into the Terror, when this happens it loses its aura of sustenance (radiant) and gains an aura of hatred (fire). At this point any followers in the area will see the truth of their misplaced worship and try to flee. When the Terror is bloodied it summons 4 screaming orbs to help defend itself.
This creature is a serious threat and you will need to put a bit of thought into designing the actual encounter surrounding it.
I have divided the 2 action points between the two form.
Arri-Vastril Savior Level 6 Solo Controller
Large Aberrant Beast (stage 1 NOT BLOODIED) XP 1,250
Initiative +6 Senses Perception +6
Aura of Sustenance (radiant, psychic) aura 10; All enemies entering
or starting their turn inside the aura take 2 radiant damage and take a -1
penalty to Will Defence; all allies inside the aura gain a +1 bonus to Will
save
HP 288; Bloodied 144; see Bloodied Transformation
AC 20; Fortitude 18, Reflex 18, Will 18
Immune charm;
Resist 15 radiant, 10 psychic; Vulnerable 5 thunder
Saving Throws +5
Speed 6
Action Points 1
[FONT=D&D 4e icons]M[/FONT]Sweeping Tendril (Standard; at-will) ♦ radiant
Reach 2; attack +11 vs. AC; 1d8+4 radiant damage
[FONT=D&D 4e icons]c[/FONT]Elegant Spinning Tendrils (Standard; at-will) ♦ radiant
Burst 1; attack +10 vs. Fortitude; 1d6+4 radiant damage; on hit target is
pushed 1 square and immobilised (save ends)
[FONT=D&D 4e icons]r[/FONT]Psychic Shove (Minor; recharge [FONT=D&D 4e icons]56[/FONT]) ♦ psychic
Range 10; attack +10 vs. Will; 1d6+4 damage; on hit target is pushed 2d6
squares and knocked prone
[FONT=D&D 4e icons]r[/FONT]Gift of Light (Standard; recharge [FONT=D&D 4e icons]56[/FONT]) ♦ psychic
Range 10; attack +10 vs. Will; 1d6+4 psychic damage; on hit target is
dominated until the end of Saviors Next turn
[FONT=D&D 4e icons]a[/FONT]Blast of Benevolence (Standard; recharge [FONT=D&D 4e icons]56[/FONT]) ♦ radiant
Area Burst 1 within 10 squares; enemies only; attack +9 vs. Reflex;
1d10+4 radiant damage; all allies inside burst gain 5 temporary HPs
Bloodied Transformation (Immediate Reaction)
When bloodied Arri-Vastril Savior transforms into Arri-Vastri Terror. Use
Arri-Vastril Terror (stage 2 BLOODIED) stats
Alignment Evil Languages arri-psy
Skills endurance +11, diplomacy +12, perception +11, insight +11
Str 18 (+7) Dex 14 (+5) Wis 16 (+6)
Con 16 (+6) Int 16 (+6) Cha 19 (+7)
Arri-Vastril Terror Level 6 Solo Brute
Large Aberrant Beast (stage 2 BLOODIED)
Initiative +6 Senses Perception +5
Aura of Hatred (fire) aura 2; All creatures entering or starting their
turn inside the aura take 2 fire damage and take a -1 penalty to Fortitude
Defence
HP 144; Bloodied 72; see Screaming Orbs
AC 20; Fortitude 21, Reflex 20, Will 17
Immune charm;
Resist 15 radiant, 15 psychic; Vulnerable 10 thunder, 10 lightning
Saving Throws +5
Speed 5
Action Points 1
[FONT=D&D 4e icons]M[/FONT]Smashing Tendril (Standard; at-will)
Reach 2; attack +9 vs. AC; 1d10+4 damage
[FONT=D&D 4e icons]m[/FONT]Thrashing Tendrils (Standard; at-will) ♦ fire
2 attacks; Reach 2; attack +9 vs. AC; 1d10+4 damage; on hit target is
pushed 2 squares and knocked prone
[FONT=D&D 4e icons]c[/FONT]Raging Heat (Standard; recharge [FONT=D&D 4e icons]56[/FONT]) ♦ fire
Burst 3; attack +7 vs. Fortitude; 2d6+4 fire damage
[FONT=D&D 4e icons]c[/FONT]Fear of the Beyond (Standard; encounter) ♦ fear
Close Blast 5; attack +6 vs. Will; 1d6+4 damage; on hit target is
immobilised (save ends)
Screaming Orbs (Immediate Reaction)
When Bloodied Arri-Vastril Terror summons 4 Screaming Orbs as an
immediate reaction, these appear adjacent to the Terror (one on each
side if possible), see seperate stats
Alignment Chaotic Evil Languages arri-psy
Skills endurance +11, intimidate +9, perception +10
Str 19 (+7) Dex 16 (+6) Wis 14 (+5)
Con 16 (+6) Int 14 (+5) Cha 12 (+4)
Screaming Orb Level 5 Controller
Small Aberrant Beast
Initiative +6 Senses Perception -2
Screams of Terror (psychic) aura 1; All creatures entering or
starting their turn inside aura take 3 psychic damage
HP 20; Bloodied 10
AC 19; Fortitude 15, Reflex 18, Will 14
Immune charm, disease, poison;
Resist 20 fire, 20 radiant, 20 psychic; Vulnerable 10 thunder, 10 lightning
Speed 0, see Follow the Leader
Follow the Leader (Standard; at-will)
Screaming Orb may shift 1 square as a standard action, this must take it
closer to the Arri-Vastril Terror
Alignment Unaligned
Str 6 (+0) Dex 18 (+6) Wis 3 (-2)
Con 10 (+2) Int 3 (-2) Cha 8 (+1)