at max stacks gain life steal. building this item with some resistence and items like Spirit Visage that stimulate the healing is very deadly combo
burns enemies, for every second in fight gain bonus magic damage up to 6%

increases healing and shielding, also health regeneration so its very good for champs like Dr. Mundo, Volibear or Warwick
out of fight for 15 secs gain magical shield. this item is very good e.g. for galio as it has really good health stats and the magic shield empowers his passive shield as well. It is also very good m ritem for any other champion of course
taking magic damage grants stacks, at maximum stacks receive additional mr and movement speed
reduces enemies mr + gives you additional mr for every cursed enemy

after using ability deal bonus physical damage on-hit, enemies withing spawned field are slowed
reduces attack speed of enemies, reduces physical damage. its very similar and cheaper option from Randuin's Omen, the only difference is Frozen Heart is used against aa champs when Randuin's Omen against critical champs like MF or Caitlyn
reduces critical damage, active slows enemies around. More expensive item than Frozen Heart but if you have enemy team comp that deals hard critical damage its very useful
deals magic damage in area around you. very solid option against heavy ad team comp
reduces healing, deals magic damage to attacking enemies. as an item with both armor and health stats its very good option for champs that scale either with HP or resistance
reduces slows, built up movement speed transforms into physical damage, slowing on you is reduced by 25%
its good item if you need your priority fed teammate kept alive because it transforms 12% of damage onto you while you will be healing and both of you contributing

gives you shield
at maximum stacks increases magic and physical damage resists
spawns zone that slows enemies and deals magic damage
quick restoration of health outside fight, gives movement speed

spawns healing area
bonus health equal to 15% mana

vs lots of cc, reduces magic damage
reduces attack damage