The boots of megi are necessary cause they give the requred minimum pen.
Cronos pendent will give you great cd reduction.(core item)
Shield of regrowth is an item thats made for change(core item)
Rod of tahuti will give you bonus damage against half health enemies which helps a lot.(core item)
Gem of Isolation, what is better then high mobility to chase enemy? running ahead of the nearly dead enemy and seeing the panic in enemy before death. Also all her abilities are aoe with her 1 being up every 1-3 seconds.(you could replace it with rod of asclepus for healing or a stacking power item like warlocks staff or book of toth for damage)
Soul Gem, think about it.... why dont you want your every 4th ability to do bonus damage and heal(you can change this for anti heal for going against helears or something else)
This build focus on harasement and running away after dealing some damage to the backline. Change is fairly squishy and requires you to keep an eye on her mana in earlygame. She will also be targeted a lot by enemy team as you will be playing in the frontline a lot.
Forget her basic attacks. Only do basic attacks very rarely when in extreme need. Use her high mobility for chase and her 2 for shifting back too the back line. Once you get shield of regrowth then her movemnt will be very fast and will allow you to evade and move about the battlefield easily. REMEMBER TO NOT DO BASIC ATTACKS AS IT WILL SLOW HER MOVEMENT DOWN. Always keep moving in random directions and stay in range of her 1 or 3 from the enemy. Her attack sequence is 1 then 2 then make some distance from enemy or keep moving around them and ranndomly changing directions. then 1 till the 3 is online again and do 3 again. also try and consentrate on their backline. use her 2 for evading or repleshening mana if you see enemy ulties or skills that do high damage. After you get shield of regrowth your 3 will give you bonus movement and when combined with 2 she can leap very far away. use her 4 when yoou are in danger, possibally being chased by their entire team or when you see 3 of their squishier characters in a group. you can also use 4 to initiate on enemy backline that have half health or less. if initiated correctly then you can 4,1,3 and then 2 out of the enemy encirclement after killing an enemy who was thinking he would be safe with half health with all his allys around.
Pros -> High mobility, High sustain, Great AOE, Can go against multiple enemies and come out alive after doing a great ammount of damage. CAn counter most assasin.
Cons -> High mana usage in early game, Certain death if stunned or routed without her 2, Enemies will target you a lot.
Assasins with Hastened katanas(These will **** you up as your mobility wont be much help)
Gem of isolation
Assasins, Mages, ADC warriors