Must-know glitches
These are some of the most common glitches, some known for about as long as the game has been released. They are all helpful in some way to achieve one of the game's goals.
Music box
The music box has a lot of associated glitches. See the Music Box Glitch section below for more information.
Free betting
The horse and dog races allow you to buy medals to bet on certain competitors. Usually, buying the medals will cost 50G each, but if you hit 
to back out of the screen instead of hitting the "OK" button, your bets will still be placed, but you will keep all of your money.
Festival rain
Festival days will always be sunny. If the weather predicts a typhoon or rain, it will be sunny, but crops will appear watered and animals will still be unhappy if left outside. In other words, the day contains all the characteristics of rain, though it appears sunny.
Dry rain
If you harvest a vegetable on a rainy day, the plant will suddenly be unwatered even though it is actively raining. You must manually water the plant for it to count as watered.
Blue Mist
If you visit the goddess pond screen any season where Moondrop flowers are blooming and water one, the Blue Mist Flower event will progress each time you exit and re-enter that screen. If you leave, then re-enter the screen three times, you can get Popuri's photo by talking to her.
Day skip
If you push a girl over 160 affection, the dream event text will occur that night. If you stay up all night and are not on the farm screen when the day resets at 6AM, the dream text will scroll, and you will warp into your house. If you check the start menu, you will see that two days have passed instead of the usual one.
Keeping crops
If you use the above day skip to skip the first of any month, the crops from the previous season will not wither. On the first of each month, crops from the previous season will wither, meaning that once you skip the first of a season, the crops will remain until the first of that season the next year. Crops will remain even through winter as if it was still their season of growing. Snowy days will not water them, but you can still manually water the plots.
Cow glitches
Cows have a number of related glitches, the most prominent ones are listed below.
Max cow affection
There are several possible typos in the programming that add to the cow's affection in situations where it would seem like it should decrease. Hitting a cow with a tool will add 20 to its affection if it changes from normal to mad, and will add 20 if it remains mad. If a happy cow becomes mad, its affection will increase by 45. If a sick cow is hit with a tool and remains sick, it will gain 20 affection.
Healing cows
A sick cow will remain sick, and will die in seven days if untreated. You can buy medicine from the Green Ranch to heal them, but there is another way. Cows have five possible conditions: normal, happy, mad, sick, dead. If a cow is hit with a tool, there is a chance that it will become mad. A cow can only have one condition at a time, so if a cow is sick, hitting it with a tool repeatedly will eventually cause the cow to become mad instead. It will remain mad for three days, regardless of food or weather, then will return to normal.
Stealing cows
This one is used in conjunction with the Day Skip glitch listed above. On Fall 30 of the first year, Doug stops by the farm and asks you if you will look after cows for a while. If you accept them, he will return on Winter 5 to take them back. However, if you skip Winter 5 by pushing a girl over 160 affection then staying up all night on Winter 4, Doug will never return to get the cows and you will keep them permanently. They become adult cows on Winter 22.
Immortal cows
If a cow is mad and unfed while indoors, it will remain mad. You can store a cow indoors while mad for as long as you want without feeding it, and it will never die.
Music box glitches
The music box is one of the most popular glitches in this game, but there are several related glitches. If you interact with the tree near the pond by the chicken coop, you will find an essential item called the "Treasure Map". You don't have to read it to find the music box, but you must have it in your inventory. Follow the directions and till the spot ten times to dig up a music box. If Rick is at least 31 affection when you talk to him, he will fix the music box, and you can give it to a girl for a +6 affection boost instead of the normal talking affection.
Infinite music boxes
As long as you don't currently have a broken music box in your inventory, you can till another broken music box, even if you already dug one up that day.
Music box disappears
If you try to till the music box while someone is on the farm or if you already have a broken box in your inventory, you won't dig one up. The music box works on a counter that increases each time you till the spot. The catch is that it doesn't loop. If you reach 10 tills and you don't dig it up because someone is waiting on the farm, the number will keep going up to the maximum of 255. To reset this counter, you have to till a different spot, then start tilling the music spot again.
Breaking Rick
If you talk to Rick while holding both a broken music box and a fixed music box, Rick will give you the dialogue where he fixes the box, but you will end up with only one fixed music box. After this, Rick will no longer fix music boxes when you talk to him with a broken box.
Character spams
Normally, you can only increase an NPCs affection once per day with a gift and a conversation, but there are several exceptions to the rule.
Karen
Talking to Karen while holding your dog increases her affection by one point, but there is no cap to this interaction. The catch is that the spam only works if the dog's affection is below 120 and her response is "it doesn't seem too clever". If her response is "It's smartened up quite a bit", the spam no longer works. If you need the spam to work, you can hit your dog with a tool to lower its affection as many times as needed until Karen gives the proper dialogue. In the Japanese version, you can look at the her face in the dialogue box. If her mouth is open, the dog's affection level is too high.
May
One of the easiest spams in the game, the conversation cap doesn't seem to apply to her. Talking to her gives a +3 affection boost that can be repeated as many times as you want. Her final speech dialogue is a single word, making her one of the easiest and fastest characters to max out affection with simply by talking to her 85 times.
Kent
Kent's affection will increase by +3 when you talk to him while holding a wild animal or a chicken. Similar to May's spam, this interaction can be repeated as many times as you want, allowing you to max out his affection in 85 interactions.
Gotz
Karen's father has an interesting spam that can't be exploited until later in the game. If you show him a baby that isn't Karen's, he will get a +2 affection boost with no cap. You can max him out with 120 interactions or get him to the party attendance minimum with 80 interactions.
Doug
Ann's father has a similar spam to Karen's father, Gotz. If you show him a baby that isn't Ann's, he will get a +2 affection boost with no cap. You can max him out with 120 interactions or get him to the party attendance minimum with 80 interactions.
Jeff
If Elli is at 130 affection or higher and you talk to Jeff at the bar, he will ask you if your relationship with Elli is "friend" or "love". If you answer "friend", he will receive a +7 affection boost. You can leave and re-enter the bar to repeat this as many times as you want until the bar closes at midnight.
Master Carpenter
This NPC doesn't have a cap to the number of boosts he can receive with gifts. Normally an NPC will only receive an affection boost for the first gift given in a day, but the Head Carpenter will receive a boost for every gift he is given in a day. Unfortunately, he is not one of the characters eligible to attend the evaluation party, making this spam useless toward getting the Party Photo.
Sprites
The sprites live in a cave in the mountains. If you enter the cave, there is a small hole behind the single sprite that will lead to a small house with more sprites. Normally, affection of a single sprite will count for all the sprites, but the sprite on the right inside the smaller cave will receive affection for gifts until the sprite's total affection is 21. You can gift this sprite just about anything, including lumber, for a +1 affection boost. The exceptions are gifts that subtract 1 affection, which are weeds, rocks, and poisonous mushrooms.
Game Crash
Doing these things will crash the game! You have been warned.
Ellens death
During Summer of the second year, talking to Ellen will trigger her death. If you throw an item on the ground, then talk to her before the "broken item" sprite disappears, the sprite will remain and the game will crash.
Hot Springs / Bridge Work
If you perform the day skip on the final day of the Hot Springs work (Winter 16) or the final day of the bridge work (Fall 27), the game will crash.
Hot tub crash
If you are in the Hot Springs when the day resets at 6AM, your character sprite will continue to swap between invisible, normal, and hot tub. If you try to sleep in this condition, the game will freeze, then crash.
Blue Mist crash
If you are holding an item when you talk to Popuri to get her photo, the game will freeze when the photo is taken.
Easter Eggs / Hidden Features
Full Moon Berry
This isn't a glitch so much as it is an easter egg. Any day between Fall 10th and 12th, the Full Moon Berry appears outside the restaurant on the mountain. If you hit "A" at the trees in front of the restaurant, you will pick up the yellow berry. It doesn't do much, nobody is particularly crazy about it, but sells for 500G.
Climb the Mountain
Before the bridge is built, it is impossible to get to the upper portion of Moon Mountain... or is it? If you hit "A" near the base of the tree near the cave, you will climb the tree and end up on the ledge on the other side of the bridge.
The Weather Vane
While in the mine (only open in Winter) and you are lucky enough to make it down to the third floor, you may dig up an object that looks like a golden chicken. This is actually an Easter egg from the SNES game that was on the roof of Ann's shop. If you show it to Rick, he will comment that this weather vane belonged to his grandmother and take it from you. He won't even give you a reward for finding it.
Invisible Glitches
There are ways to turn practically anything invisible from your possessions and items to your animals and other people. There are even ways to make yourself invisible. Be careful, though, as, in some cases, invisibility is permanent. Make sure to save before you try any of these (unless you prefer it the new way) and don't save after.
Disappearing Dog
This glitch technically doesn't turn your dog invisible, but it will make him disappear forever. Pick up your dog and set him down in your bathroom. He will wander around for a while and eventually hop off into the darkness never to be seen again. He will still make noise, but he will never come back.
Invisible Horse
Ride your horse around your farm until 6:00am. At this time, you will be teleported back into the house. After snacking on your morning sushi, you will be riding your horse. When you jump off, it will become invisible. You can ride it around, but you can never take it outside and it will remain invisible.
Invisible Baby
When your baby is old enough to leave the crib and move around on its own, pick it up and walk to your bathroom. Set it down just outside the door. Pick it up, then open the door the bathroom quickly. If you do it right, you will emerge from the bathroom holding your baby, but he is invisible. If you press 
to identify what you're holding, it will say your baby's name, but nothing is there.
Invisible Main Character
Wait around your farm until it's almost morning. Just as the clock hits 6:00am, jump into the hot springs. If timed correctly, the game will reset the next morning while you are in the spring. After eating breakfast, you will switch to being wrapped in a towel, invisible (with a shadow), and normal randomly as you run around. If you try to get in bed to save the game, your character will be invisible under the blanket.
Continuity Glitches
These glitches seem to give your character superpowers. Do you want to walk through walls? Fly over trees? Well these glitches are for you.
Jump off the Farm
If you arrange two stumps diagonally on the edge of the farm (see the picture to the left), you can jump over them diagonally and off the page. You'll land in the black, free to explore the dark expanse surrounding the farm.
Stomp the Trees
At the top of the ramp going to the vineyard at the crossroads outside your farm, instead of going to the right into the vineyard, walk up and to the left. You'll walk up and into the black region. Walk to the left and down over the trees or go up and into town.
Windwalker
When the bridge is complete, you can still cross the gap without the bridge. Walk into the left post of the downhill side of the bridge. If you run towards it and slightly left, you will eventually run out over the chasm.