You need a fully coordinated team for a medusa to work. The supports must be constantly stacking ancients and hard camps for you to clear with mystic snake/split shot.
Also, linkens is a truly terrible item. Rushing a Manta on Medusa is the absolute best. Manta into a Skadi gives you all the stats you need to boost your Mana and health pool in the mid game due to the 3(!!) ultimate orbs you use. After that, I usually go for Butterfly into a Satanic and then a Rapier. Evasion+Lifesteal+Ridiculous tank potential from mana shield and your high health will make you feel truly immortal, and unless the other team has been steamrolling yours, you will be, thats why Rapier is the ebst choce for a damage item, think flak cannon but permanent.
Thing is, your team must hold on to your base for at least 35 mins for medusa to start feeling scary, and even then you shouldn't join a fight unless it's truly necessary. She's like AM but without the split push, you play a farming game where you try and secure the late game with your ridiculous farming potential. She can also push very well due to her manta illusions having split shot.
Edit: also worth noting, if you are not gonna build a Rapier, you must replace one of your items for a damage item. Medusa has very abd Stat gain, particulary Agility for a carry (2.5), which means you don't scale with levels, but with a truckload of items. Butterfly Manta MKB and Daedalus should be enough if you're going the damage route, but at least get eithera Skadi or a Satanic, preferably a Satanic since it gives you an extra life.
