Alice is a shapeshifter character with a versatile playstyle who can be either a scary attacker or a though defender. The Jabberwock is one of the best sidekicks in the system and Alice has access to healing which is rare. On the flipside, this comes with moderate HP and overall below average deck-consistency. She has a chance against anyone but her inconsitency keeps her around the mid, below-mid tiers on power level.

Her HP is below average but 8 HP for a sidekick is tied for the most and the best in this version.
15 unique cards is too much and the reason for inconsistency. Both her attack and defense values are slightly below average but your form will help.

It is one of the best sidekick in the game due to its amazing unique attacks and high HP.
Both its unique cards, Claws That Catch and Jaws That Bite are big threats which cannot be ignored. Also it can act as a meatshield when you're big.
Alice's special ability is the best in the 1st set. She can be big. That gives you an unfeintable +2 damage to all of her attacks. Or she can be small, which makes all of your generally mediocre defense cards better with +1. In theory you want to be small on defense and big on offense.
You can only change form by cards and those effect are not optinal. Managing the form well makes an okay Alice a great one.
Generally speaking you want to start the game big if you can make the 1st attack. (Usually the starting player does so) And as small if you'll get attacked 1st. (As player 2). But your cards matter a lot here so this is not set in stone.

Snicker-Snack has a sick effect. Discarding a card from the oppenent's hand is already a good effect but choosing their current best card is fantastic.
What you want to choose depends on the hand and the current state of the game, of course, but generally the priority:
Arthur

• Excalibur - he is way less scary without it and has only 1 copy
  
• The Lady of the Lake - so he cannot recycle the Excalibur
  
• Any better 1 copy cards such as Prophecy, Aid the Chosen One, The Aid of Morgana

Medusa

• Hiss and Slither - her best defense and you don't want to discard cards anyway
  
• Second Shot - one of the scariest attack in the game
  
• A Momentary Glance - avoiding auto-damage is always great

Sinbad

• Voyage Home - his most important card
  
• Exploit or Leap Away - his highest valued defense cards and usually you care less about Feints
  
• Commanding Impact - his best non-Voyage attack and the only good one that the Porter can use

Your other good offense cards.
Momentous Shift can be a 7 attack card when you're big while O Frabjous Day! is a safe 6 attack card which turns you small.Looking Glass is a felxible defense card that usually heals you and draws cards. On rare occasions it can also teleport you anywhere on the board. This will be handy against ranged opponents so you can suprise attack them on the next turn. Also good to escape pins. Manxome Foe is an important card because it is a scary offensive weapon that can be used by Alice and The Jabberwock as well. Your average boost value is around 2.3 so on average it is a 7 attack card while you're big. The effect is not optional so you're going to lose a card. This can be painful during long games. While usually this is an offensive card, can be a strong defense even as big Alice.

Arthur is overall quite weak. Snicker-Snack is really strong against him. His defense is lackluster so going in is a good option. You'll have a card advantage. Burning his defense works. Be careful when you're big and don't have a Feint in hand, he can hurt you really bad. Killing Merlin early on is good option. He is a good sidekick and without him Arthur is even weaker. If you fall behind in cards, move away and refill. Your boost values are better, so he won't catch you easily. He can't easily kill the Jabberwock either. If you can corner him while you're small and pressuring him with the Jabberwock, do it. You'll outlast his offense.
Not going to lie, this is a tough matchup but you'll still have a better chance than the most of the cast (not just in this digital edition). You'll have to fight your way throgh the harpies. Those little bastards are annoying. Try to not get hit by her ability. She cannot ignore the Jabberwock but she can kill it, so you must defend your sidekick. Killing the harpies with Regroup while you're big can refill your hand but most of her defense cards are 3s. So better use regroup as a bait. Bait those Feints and Hiss and Slithers so you can use your Snicker-Snack and Jabberwock attacks safely. Feint is a great card against Second Shot. Never let her attack you without spending a card on defense. Gaze of Stone is a threat that cannot be ignored. Teleporting with Looking Glass is a good option against her.
This is a slightly Alice-favoured matchup but not by much. He is really weak early on. Pressure him until 2-3 Voyages came out then try to be defensive. In the late-game he is a monster. Don't use Feints early on unless you don't have other defense option in hand. Most Sinbads want to use Voyage Home as the 6th or 7th Voyage card. This make him really vulnerable against later Feints and Snicker-Snack. Porter is a bad sidekick. All he does is some card-draws which Sinbad doesn't need anyway. You can ignore him on most of the maps.

Alice is a really fun character to play as. She's often used as a power-check for newer released characters. The deviation in her matchups is pretty low. She can beat anyone but her average win-rate against most opponents is only around 45%. This makes her a B/C tier character but in this version of the game she is the 2nd strongest behind Medusa.