Medusa is a monster both literally and figuratively. She has been one of the top character even after many releases. Her discard theme makes the opponent exhaust faster while she can poke you from range then turtle behind the harpies. Or just simply run with her great movement. Her playstyle is not flashy but very effective.

Her HP is average but the range, movement and overall better defense makes her hard to kill.
She has a really consistent deck, with only 11 unique cards. Even her low attack value is deceptive.

1 HP sidekicks but you have 3 of them and can resurrect two during the game. Unlike Medusa, they are melee fighters. Their role is mostly defense. Can act as a wall between you and the opponent or just pin them in a spot and poke them until they get through the Harpies.
Their two unique cards are The Hound of Mighty Zeus and Clutching Claws
Usually, The Hound of Mighty Zeus is an attack. Run in, then step back to safety or just pin them. 4 attack is good to burn some defenses, but this is your better defensive option also. Clutching Claws is okay. 3 block for a 1 HP sidekick often not enough to save them and 3 attacks is just mediocre. However, the effect is good and you'll get it unless it gets Feinted.
Medusa's special ability is a simple one. At the start of the round you may deal 1 damage to an apposing fighter in your zone. Fortunately, the client doesn't let you forget this :) Multi-zone spaces are covering a lot of the map, making hard to run away from this ability. However, be careful standing on the edge of a zone. A melee character can attack you from and adjecent space while being safe from this ability.

I considered Hiss and Slither but not much to be discussed there. On the other hand Second Shot is your best attack card. You almost always want to boost this. Feinting this is not that bad either because you don't have to commit before. You have multiple 4 and 3 boost cards to fuel this. Most of the time Gaze of Stone is your go-to option.
Hiss and Slither is one of the best defense card in the game. The effect is not random, still card advantage is great. Try to not get baited by a Regroup.Gaze of Stone is an ongoing threat that forces your opponent to block every single attack Medusa does. The risk for a 9-10 damage attack is too high. It is really hard to win a battle with a 2 value attack, so this effect rarely will be solved. Since it has a boost value of 4, makes a great fodder for Second Shot. Sometimes for mind-games I use 1 just to remind my opponent I can do this.A Momentary Glance deals 2 direct damage to anyone in Medusa's zone. You have two copies so this is 4 auto-damage. That is fantastic finishing off low-HP sidekicks or pushing exhaustion further. Against opponent without any heal you can safely use this anytime. This is your other card with a boost value of 4, making an option for Second Shot.

Generally Medusa has only a few hard matchups and those characters are not available yet.
Killing the Jabberwock is a priority. Its Jaws That Bite can kill two Harpies or kill one and damaging you for free. Always have some defensive options in hand even when far away. Looking Glass can teleport her next to you. She has hard time catching you late-game if you try to stay away. Small Alice isn't scary but I'm Late, I'm Late can move her 5 spaces and change size for a huge swing turn. So it's better attacking her on your 1st action. Against big Alice Hiss and Slither, Feint and Dash will do the job.
Consider killing Merlin early on. Try to pin Arthur with the Harpies in a spot where you can attack him with Medusa. If you have only 1 Harpy or none you can simply stay away in safety. Arthur's movement is terrible. His boost values are bad and cannot afford to spend much cards on that anyway. The longer the game goes the better chance you have. Discard is even better against him because if he wants to use his ability he has to burn two cards. Try to spread you Harpies. Restless Spirits can kill two of them.
Unlike others, Sinbad is a character you cannot run away from. Surrounding yourself with Harpies still can maintain safety. Save Feints for mid/late game. If you can feint Voyage Home the game is done and gone. But feinting any Voyage is good. He has a lot of card draws, so discard is less effective, but not pointless. He can even intentionally discard some of the worse Voyages early on to ramp up quickly. His defensive options are limited and due to the immense draw-engine he will exhaust himself sooner than you. Most of the time the Porter is not a threat.

Medusa is one of the strongest charater was ever released. She has no obvious weakness and has many strength. Her movement, discard-package, auto-damage and range makes her even pretty easy. Medusa has an average 65% winrate against the roster which puts her into S tier. This is even better if you consider all her challanging matchup (T-Rex, Elektra, Sherlock) maybe never will be implemented in this version of the game.