If Mordekaiser is gaining no CC and limited Mobility Riot should focus on making him immortal
http://www.surrenderat20.net/2015/02/213-pbe-update.html#mor1
Changes made are based on edits to the changes on the PBE currently so keep that in mind
The general idea is if Morde is truly going to remain immobile he should become relatively immortal as well
Give him the niche of "Literally the most obnoxiously unkillable thing out there"
Made with this general build in mind:

CDs and damage mostly lowered across the board
General: Base stats lowered quite heavily due to his Shield generation and amount being almost 50% higher than on live
- HP reduced to 500 - 1800 from 555 - 1915
- Regen reduced to 0 - 0 from 8.4 - 17.7
- Armor reduced to 20 - 70 from 24.9 - 84.4
- MR reduced to 30 - 30 from 32.1 - 53.4
- Range increased to 175 from 125
**Passive: ** Morde now regens health based entirely on shield strength and shield strength is directly tied to his Max HP
- Shield strength adjusted to 30% of Max HP from 90+30*Level
- Awards Mordekaiser base health regen per second equal to 2/4/6% of his current shield strength (Levels 1/7/13)
- Shield decays by 3/6/9% per second when out of combat for 4/7/10 seconds (Levels 1/7/13)
- Shield generates based on Max HP and is 30% less effective against Minions
- Health costs are subtracted from the Shield before Morde's health
- Basic attacks generate shield based on 1% of Max Health, doubled on Mace Hit and Quadrupled for Isolated Mace Hit
Q: Damage centered around Total AD instead of Bonus AD
- Health cost adjusted to 2/2.5/3/3.5/4% of Max HP from 25/32/39/46/53 flat
- Gives 2% of Max HP as passive shield per target hit, doubled if target is Isolated
- CD reduced to 7/6/5/4/3 from 8/7/6/5/4 seconds
- Damage adjusted to 120/130/140/150/160% Total AD from 80/110/140/170/200(+40% AP)(+100% Bonus AD)
- Damage increase when Isolated reduced to 50% from 66%
W: Instead of MS increase he awards a shield based on giving up a percentage of his passive
- Health cost adjusted to 6/6.5/7/7.5/8% of Max HP from 26/32/38/44/50 flat
- Converts 10% of current Passive Shield into a Health Shield when placed on Allies
- No longer gives Allies Armor and MR
- Armor and MR adjusted to 10/12.5/15/17.5/20(+10% of current shield strength) from 10/15/20/25/30
- Armor and MR scaling bonus is doubled if Self Cast
- Converts a total of 20% of current shield strength (aka removes 20% of it for this effect)
- Casting on Allies will also give it to Morde
- Gives 1% of Max HP as passive shield per second per target hit
- PBE change of giving flat MS removed
- AP ratio increased to 140% from 20%
- CD reduced to 16/15/14/13/12 seconds from 20/18/16/14/12 seconds
E: Most spammable ability also gets highest cost because it can also generate shield instantly and it gained a Max HP to damage ratio
- Health cost increased to 7/7.5/8/8.5/9% of Max HP from 24/36/48/60/72 flat
- Gains 3% of Max HP as passive shield per target hit
- Damage reduced to 60/90/120/150/180(+10% Max HP) from 70/115/160/205/250(+60% AP)