Five of the 28 are the five bosses, and a dozen more unlock simply by playing. The interesting ones are those where the description hides a threshold.
The seven with a number behind them
The game checks an exact value for these. Three of the numbers are in the Steam description (the 100,000 sale, the 10-second kill, the one-hour finish); the other four are not, and the rule behind each is set out in How do achievements unlock?.
Impressive wants a combined kill multiplier of 5. Bonuses multiply rather than add, and no four of them reach 5 on their own: Explosion, 360, Longshot and Headshot together are 3.66. The route is five bonuses on one kill, because the fifth adds Impressive itself, worth double, and the product passes 5 with anything left over.
Rich! Millionaire wants a single sale of 100,000 or more. That figure is the final price, so the weight roll, the cooking multiplier and every kill bonus count towards it. A boss sold at a high weight roll and a good kill is the realistic route.
Easy wants a full boss dead inside 10 seconds of it appearing. Mini-bosses do not count, and
the large bosses are out of reach: a maxed shotgun needs 26 shots on the Pufferfish from a
two-shell magazine. Pick a small one instead. The 
Spider CrabSpider CrabSells for$10,000Health750Weight4.5 kg – 31.5 kg has
750 health, two maxed shotgun shots or five maxed pistol shots; the
Giant PiranhaGiant PiranhaSells for$11,000Health2,500Weight1 kg – 7 kg has 2,500, four maxed shotgun shots with one reload.
Both are summoned with cheap quest baits, so a retry costs little.
Handyman wants the hit that empties the last boss’s health bar to deal under 5 damage. Bring the boss down to a sliver first, then finish it with bare hands, or with one pellet of an un-upgraded Shotgun, which does 3 per pellet; the game checks each hit on its own.
Bean wants the game finished with under an hour of total playtime. It is measured against saved playtime, so it survives across sessions but does not forgive a slow first run.
Yummy in my tummy wants a creature cooked past 1.5 on the grill’s scale, which is beyond the point where cooking stops adding value. You have to deliberately ruin one and eat it.
I’m the bird now wants the boat at a height of 10. The description says “make the boat fly”; the number is what the game measures.
Where are you in the game?
Still on the first islands
Take the ones that come with the story and the first purchases, and set up Noob early: a kill with no other bonus at all, which is easiest with a plain melee hit on a common catch.
Mid game, islands 3 and 4
The grill carries two (Grillmaster for starting it, Yummy in my tummy for eating a burnt catch), the casino two (All in for a green win, GOLD GOLD GOLD for a legendary skin, and the Reel is available from island 2), and the Albatross one (Terrorizing bird). Competitive eating wants any mini-boss eaten, and Vacation is the Pufferfish itself.
After the credits
The four long ones: both journals, the 100,000 sale and the one-hour run. Bean is measured against total saved playtime, so it needs a fresh save played straight through.
Everything, in order of when it turns up
| Achievement | What the game asks for | What that means in practice | When |
|---|---|---|---|
| Getting started | Kill your first creature | Any creature counts, including a crab off the starting rod. | Early |
| Drip | Kill a drip creature | Every non-boss catch rolls a flat 10% chance to arrive as a drip variant. | Early |
| Who stole my beer | Find and kill the culprit, and bring it to the lighthouse keeper | The island 1 boss. Buy a Beer, hand it over for the Empty Beer Can, then fish the Spider Crab. | Early |
| Getting an upgrade | Upgrade the engine on the boat | Buy the first motor, sold from island 2 onwards. | Early |
| Noob | Get a kill with no kill score multiplier | Awarded when a kill earns no other bonus at all, which the game marks with its own 1.01x Noob Kill bonus. | Early |
| Dinnertime | Catch dinner for the lady in the forest | The island 2 boss. Hand in three Leeches for the Leech Bait, then fish the Giant Piranha. | Mid-game |
| Let me go | Get picked up by a seagull | A seagull has to pick up your body after you die. | Mid-game |
| Impressive | Get a 5x killscore multiplier | The combined product of every bonus on a single kill has to reach 5. | Mid-game |
| Grillmaster | Start the grill | Complete the island 3 grill quest with a Blue Shark or a Goblin Shark. | Mid-game |
| Vacation | Help the tourist swim on his vacation | The island 3 boss. Hand in one of the seven accepted creatures for the Carrot, then fish the Pufferfish. | Mid-game |
| GOLD GOLD GOLD | Unlock a legendary skin from the slot machine | One spin in ten lands on the machine's single legendary reel slot. | Mid-game |
| 360 no scope | Kill a creature with a 360 no scope | Both bonuses have to land on one kill: a full spin just before firing, and firing a scoped weapon without aiming. | Mid-game |
| I am speed | Buy the best engine for the boat | The second motor, sold from island 4 onwards. | Late |
| Fully equipped | Apply all attachments to a single weapon | One weapon needs a sight, an ammunition upgrade, a barrel attachment, a laser sight and the extended magazine at the same time. | Late |
| Terrorizing bird | Defend the scared islanders from the terrorizing bird | The island 4 boss. The Albatross is not on any bait table, so there is nothing to buy for it. | Late |
| Yummy in my tummy | Eat a burnt creature | Eat something cooked past 1.5 on the grill's scale, which is beyond the point where it stops being worth more. | Mid-game |
| Deadliest catch | Help the military defeat the big creature they located | The island 5 boss, and the end of the story. | Late |
| We are so back | Finish the game | Awarded on completing the final quest. | Late |
| All in | Bet on green and win at roulette | Green pays 35 times the staked item's value, against 2 times for red or black. | Mid-game |
| Easy | Kill a boss within 10 seconds | Counted from the moment the boss appears, and only full bosses qualify, not mini-bosses. | Late |
| I'm the bird now | Make the boat fly | The boat has to reach a height of 10. | Mid-game |
| Competitive eating | Eat a mini-boss | Any of the six mini-bosses, eaten rather than sold. | Mid-game |
| Rich! Millionaire | Sell something worth 100,000 or more | The figure is the final sale price, so the weight roll, the cooking multiplier and every kill bonus all count towards it. | Late |
| Collector | Find and kill all the creatures | Every creature the journal tracks. Five creatures you will certainly catch are not tracked at all. | Late |
| Everyone's dream | Kill a seagull with dynamite | Dynamite is sold from island 2 onwards. | Mid-game |
| Handyman | Defeat the final boss with your bare hands | The hit that empties the health bar has to deal under 5 damage, and hits are checked one at a time. Bare hands qualify; so does one pellet from an un-upgraded Shotgun (3 per pellet). Brass Knuckles start at exactly 5 and fail. | Late |
| Fishipedia | Find and kill all drip creatures | Every creature the journal tracks, caught as a drip variant. | Late |
| Bean | Finish the game within 1 hour | Measured against total saved playtime rather than one session. | Late |
The two collection achievements
Collector wants every creature the journal tracks. That is 49 entries, and five creatures you will certainly catch on the way are not among them.
Fishipedia wants all of them as drip variants. Worth knowing before you start: in the shipped build the drip roll is skipped for anything carrying a boss tier, and those eleven journal entries ship without a drip model at all. We could find no path in the build that marks a boss as drip, which is our reading of the code rather than a statement from the developer.
Finishing the Fishipedia lists exactly which creatures each half wants.
Next Two of the seven threshold achievements come down to the kill multiplier. The money guide lists every bonus and what it is worth.