here's some tips that could be helpful, (also i beat it)
destroy everything- the more loot the better, you don't have much without farming so you need to loot all the food you can, this'll mostly be wildberries and berries, so you want to make sure you don't get hit much
doortrick- repeatedly attack a door in a room, this makes the room load in and out constantly and essentially is slow motion, so when things go toward you it's very hard for them to make it to actually hit you
slimes- just be careful not to get hit by their jumps, otherwise easy
bats- erratic and fast, but very important since they often drop wild berries
skeletons- just walk toward you, just spam hit, only bad in groups, also don't get knocked back much
big slimes- same as slimes, just have more health
marble golem- same as skeleton but more health, when in a room with a wizard it's easier to slowly funnel them out
wizard- trap them in a corner while they're shooting at you and spam hit while they're shooting fireballs so you don't get hit by one, and make your way to them and spam hit them in the corner (fireballs bounce off of marble golems)
gar- The most stressful part! don't try to make it go faster by going for a bunch of risky hits because that'll just put you at a high risk of loosing all the progress you've made. paitence is key in this battle. you won't do much damage, the most damage you'll do is when gar spawns near a corner. you should try your best to hit through the fireballs without taking damage and spamming hit while he's stuck in the corner until he teleports out. make sure there isn't many fireballs flying around in the arena, they can be risky to leave. don't get cocky, and use food sparingly but not so sparingly that you end up dying because you didn't eat. with some luck, skill, paitence, and these tips, gar will be dead! and you've won the challenge!