Here are my thoughts: Increase MS to 345, gains MR per level, small boost to HP/HP per level.
Passive:Feint
Shen is a ninja, and is thus a difficult target to pin down in a fight. His quick reactions and movements and keen senses allow him to roll with the punches and avoid damage.
Shen takes 6/8/10% less damage from basic attacks (levels 1/6/11) and Area of Effect Skills. After taking damage from 10/9/8 such attacks (levels 1/6/11) Shen gains stealth and the ability to move through units for 2 seconds. Activating a skill or attacking breaks this effect immediately.
Passive: Shadow Strike
After Shen enters stealth, his next attack within 5 seconds deals dmg to all nearby enemies (range: 250?), slowing them by 50% for 2.5 seconds.
Thoughts: This new passive allows for Shen to remain tanky, while also having the ability to reposition in combat. It rewards him with "ninja flare" for doing his job, being the front line and protecting his allies.
Q: Vorpal Blade_____Cost: 50 Energy________Cooldown: 8 seconds
Shen throws one of his swords in a straight line (Im thinking 600 range) that deals 80/120/160/200/240 (+50% Bonus AD)(+30%AP) magic damage to the first target hit, marking them and revealing them to Shen for 5 seconds. While marked Shen may reactivate this skill to cast Retrieval.
Q: Retrieval_______Cost: 25 Energy (Q's cooldown starts after this is cast, or the target is no longer marked)
Shen appears behind his target and rips the Vorpal Blade from them, dealing magic damage equal to 6/7/8/9/10% of the targets max health and healing Shen for the same.
The vorpal blade drinks the life of its targets and returns it to its weilder
THOUGHTS: This makes the skill more dynamic and fun to use. Grants him some fun uses, potential engage, escape, and feels ninja like when you just appear behind him. It gives him some decent sustain, but not over bearing and not as constant.
W: Ki-Strike_____ Cost: None____________Cooldown: 10/9.5/9/8.5/8 seconds
Shen's next basic attack deals bonus magic damage equal to 50% AD plus 10% Shen's bonus health. Hitting an enemy champion will restore 20 energy. Basic attacks against non-structures reduce the cooldown of this ability by 1 second, doubled vs Champions. If used in conjunction with Shadow Strike, the duration and power of the slow is increase to 65% for 3.25 seconds. Hitting multiple enemy champions does not restore more energy.
THOUGHTS: As an auto-attack reset, this should increase Shen's dueling power, as he can save his Ki-Strikes for the right moments. He can use it immediately for 1v1 dmg output, or save it for when his passive stealth procs to try and get a bigger slow on targets.
E: Shadow Dash________Cost: 120/110/100/90/80
Shen dashes a short distance (450) and deals 50/80/110/140/170(+60%AP) magic damage to all enemies he hits. Hitting enemy champions refunds 50% of the energy and taunts them for 1/1.25/1.5/1.75/2 seconds. While taunted, enemy champions must auto-attack Shen and Shen takes 50% reduced damage from them (DR applies to auto attacks only). Hitting multiple enemy champions does not refund more energy. The distance Shen dashes is increased by 50% of his bonus movement speed.
THOUGHTS: Ghost synergy anyone? :P Mobility tank is what I like here. Running from a ninja should be difficult.
R:Eye of Twilight/Shadow Protector
Passive: Eye of Twilight: Whenever Shen is stealthed (via his passive) he reveals invisible/stealthed units and traps within 500/550/600 range.
ACTIVE: Shadow Protector: Shen enters the realm of shadows, becoming untargetable and granting a shield to nearby allies (1000 range) equal to 10% of his max HP for up to 5 seconds. While he remains in the shadows, shielded allies can see invisible/stealthed units and traps within 300 range of themselves. The first time an allies Shield is broken, Shen leaves the shadows and appears next to ally.
THOUGHTS: This new ultimate would keep Shen as a team fight protector. The rest of his skills would still make him an effective split pusher, but doing so means his ult has less use. If Shen is supposed to be a ninja tank/protector, he should need to be with his team to do so. Split pushing should have a trade off.