I need help on building Medusa. Standard build to most is probably a mix of linken, butterfly, manta
But there are few problem to this build 1. Split shot reduction takes into account of damage from agility, that means direct damage like DR is the best. Linken, butterfly, manta all suffers from this problem. 2. Cost per damage output is too high. 3. For a carry, a BKB is generally more useful than Linken's, except that Medusa benefits greatly from all the stats it gives. But it's not really useful it team fights where spells are all flying around.
There's another way of item build advocating battlefury. It gives regen and direct damage though the cleave is wasted on a ranged hero. By getting this, Medusa is forced to get BKB as next item and becomes very reliant on it due to her items lacking of HP/MP boosting items. Extension likely to include anything to boost her HP/MP like Skadi. In that it sacrifices her late game prowess, unless you rebuy BKB.
Optimally, split shot increases your DPS by a factor four.
As split shot works on manta, it's one of the best dps items to get for her, you basically get 224% damage of your agi as damage from the illusions compared to the normal 56%. So agi routes are the way to go, if you don't want to man up and go for DR.
Manta Butterfly Skadi
Is probably the build I would go for. Linken, if you need the block. MKB if you face evasion, it allows all your shots to get true strike. Satanic if you need lifesteal. Eblade if you want pure agi.