With the exception of Ice, you should only do the final collection achievements after you have beaten the game and all the modes. I recommend completing the modes in order of Pacifist -> Standard -> Tougher Enemies -> Double Trouble -> Idle/Evil.

It is best to go for these achievements in Pacifist Mode. The 10x multiplier for the auto gather makes the speed at which you scale significantly faster than other game modes.

Except for ice. You just need one completed game mode.

For completing game modes that require you to fight difficult enemies, I recommend a core of Nyx with the Sorcerer's Staff, Tankston with the Healer's Hood, and Hearth with the Revival Draught. Hearth should also have Shadow Scythe if she can equip multiple items, as her Shadow will also have the revive ability and a decent chance at reviving the real Hearth.

You can use recommended build for the Party Talent, Skill Caster for Nyx, Meat Shield for Tankston. For Hearth, select Heal and Revive Focus, immediately deselect it, refund all points involving the skill, and max out the revive skill traits instead. Then put the rest of the points into health.

For auto battle actions, set Tankston Special to Always. You may also need to set TickTock Special to Only if Maxed, as sometimes you get stuck in a loop where she just keeps spamming it while you do no damage.

The other characters I prioritized were Shieldra with Pure Tank, TickTock with Team Support, Buffy with Buffing Tank, and Cleanse with Cleansing Tank. The last slot was flexible, but usually another tank. I liked Thor with the copy focus (just copy whoever you need. his special makes everyone the same character but also revives everyone, but it's an edge case.) or Chop with Bleed Damage build.

Spirit points should prioritize Bonus Attack Damage and Armor for the early game so you can deal with the Resist slimes without having to think too much.

Later, prioritize speed and health so the units can survive incidental debuffs.

This set up should allow you to autobattle most fights.

Once you unlock Mortimer, he can replace Nyx for fights with multiple enemies with Special Focus.
Once you unlock Morgana, she can replace Buffy and Cleanse with Special Focus.
Once you unlock Blair, you can use her Special Focus and have her be the solo damage dealer.

If you have trouble with specific fights, you may have to modify builds somewhat by taking points out of the prioritized infinite scaling and put them into health instead. Keep in mind you will have to deselect the preset build, as the next time you get a party point, it will undo any changes you have made and change it back to the preset build. If there is no preset build, the points will no longer be automatically added as you get them.

You should prioritize Health late game as most deaths at this point are due to randomly dying from debuffs. Most early fights are defeated by Tankston healing and Nyx debuffs. Most late game fights are defeated by debuffs or Blair killing everything, while Hearth lets you grind out multiple waves by constantly reviving two allies.

Easiest by far, only requires ONE game unlock.

Scaling: Upgrade Shot ( x2 multiplier which is completely insane), Extra Ammo, Bonus Blocks (doesn't matter lol)

Early set-up: Use upgrade shot. Get magnet and multiplier. Unlock weapons. Unlock extra ammo and Blinkie Moves! You want to find extra ammo upgrades, use upgrade shot in a nook somewhere, then collect the ice with magnet.

Mid set-up: I prefer using orbs to clear entire sections. Basically you just need to choose an ice level that orbs can one shot. Collect as much extra ammo as possible. Find a nook and spam upgrade shot. Destroy it and collect the ice with magnet.

Late set-up: Literally the same except everything is leveled, you can go to ice level 25, obliterate everything except for one small section, then use an upgrade shot 60+ times in a deliberately left nook, then collect it with a magnet.

Edit: Below may be fixed now with +99 max bonus limit.

If you set the notation to scientific, it is possible to hit overflow and get NaNeInf that bugs out the game in multiple ways and causes frequent crashes when you try to interact with too much Ice. You won't be able to change back to any other notation without crashing, so I do not recommend doing this. If you stay in standard notation, I think the NaNeInf ice just gives you nothing instead.

Second easiest, but requires 4 game unlocks, although it is way more difficult to consistently hit targets without the 5th game unlock bonus.

Scaling occurs from Boss Bonus (2% per boss per level), Laser Damage (only way to kill later bosses), Target Multiplier (4% per target hit).

Your goal is ~45 Boss Bonus, ~35 Laser Damage with everything else basically maxed out. Always try to hit targets to scale. (And at least 120 targets hit)

Early setup: Rush Blinkie's Basket upgrade. Add time, then more apples, time bonuses from killing, dash wave, turrets. Get Boss Bonus, and upgrade time skip with laser damage.

Mid setup: Max out everything in general, but prioritize maxing time skip, laser damage and boss bonus.

Late setup: Once you consistently reach the final boss slimes who one shot you, you will need to change tactics a bit. Disable Heal, Ice, and Fire Turrets. You should have maxed shock bounce by now. Optionally, you may choose to refund laser width for a bit more control over boss killing. You want to start maximizing your scaling.Whenever you face against a solo boss, focus on targets instead of killing bosses as quickly as possible. If possible, use the laser to kill all but one boss in the multi-group, then let the turrets/incidental fireballs slowly wean the boss down while you use the time to kill extra targets.

When you reach the five ice bosses, the boss right before the final boss, the final bosses will spawn extremely fast with only a two second delay or so between each wave. It's best if you keep one ice boss alive, kill it with the first tick of the laser, then use the remaining duration to one shot the next three waves of the final bosses. This is extremely important. You should be able to kill 9 bosses with one laser and get the boss multiplier 9 times.

Third easiest, but also requires all 5 game unlocks. If you don't have the magnet upgrade, it's hard to get the final value high enough to scale well with the octopus.

Scaling is Henry the Octopus and Brethren (5% per brethren)
Lesser scaling is Golden Multiplier and Golden Hook/Mine Multiplier.
Your goal is at least 14 Brethren upgrades.

Early setup: Prioritize gold fish and their multiplier, trying to get as deep as possible with hook weight for more expensive fish to multiply. Rush to unlock the power-up Anti-Red fish and get the red->blue and blue-> gold.

Mid Setup: Magnet+Anti-red+Mines+Brethren.

Late Setup: Magnet+Anti-red+Brethren. Near the top, hit mines and collect power ups. You want to use power ups that are not magnet or anti-red until you have a mix of both in your power up storage. Continue hitting mines and power ups until anti-red or magnet triggers. Then use up all of your power ups, rush to the bottom while avoiding mines, collect and use every power up, and let magnet collect everything instead of the mines.

You may have to reset if you get unlucky with early powerups.

4th hardest minigame, but has a very high floor, although its late game scaling is slow and comparatively tedious.
Also requires all five unlocks, as if you don't have Blorbs on Blorbs, getting maximum value out of Blorbs is very annoying.

Scaling: Level (Flat x7 multiplier at level 7), Baddie Level (1+(.25 per level)), Blorbs (about 70% per blorb if you get all 10 bonuses) Time bonus falls off really hard. Higher levels also give a much higher base amount of crystals.

Early set-up: Try to get to level 7 ASAP with Grofl. I think if his base damage is lower than half the current health of the target, it sets his damage to exactly that, so he ignores scaling somewhat. This allows him to quickly destroy the exit gates. I like to get Better Map asap, so I can reset if Grofl is far away.

Mid set-up: Ramp up the baddie levels. You can go up baddie levels earlier than you may think because of Grofl. At level 7, try Baddie Level 10. With Grofl, you should be able to kill the first enemies in 1 or 2 hits depending. Then rush to the exit. You can repeat this with higher and higher Baddie levels as long as you are able to find Grofl and kill the enemies in one or two hits. There is a cap in this quick leveling around Baddie Level 53. If you haven't unlocked blorbs yet, you can stop here, it should be more than enough crystals for now.

Late set-up: This part is annoying. Because Blorbs scale so well, you NEED to stay for the full 10 minutes and hit all the Blorbs. If you hit 9 minutes of blorbs 10 times each, that's more than a 10^12 multiplier. You can also hit the entrance at the last second for a final 1.25 multiplier (this multiplier only applies if you exit with the staircase).

Once you have enough damage scaling, skill damage, status effects, etc. then you can go up baddie levels. Try 5 level increments starting at 55. Unfortunately, you won't do enough damage to quickly kill anything. Instead, you need to collect everybody as fast as possible with dashing, then run around in a small circle hoping something dies. If you do not kill anything within 90 seconds or so, you set the level too high because you don't have enough damage upgrades. You are basically waiting for poison damage and Grofl to bring anything low enough that status effects are able to deal the rest. Even if you miss out on about a minute of blorb scaling, the base crystal amount is more important.

Your goal is about Baddie Level 80, although slightly lower may barely be enough to hit the 1 decillion threshold.

There is a tactic that may allow you to tackle higher Baddie levels with a bit of RNG. Don't give freeze to anybody. Collect everyone except for Chill. Then go around in a small circle or back and forth, using dash as needed. Your goal is to make enemies walk on the poison puddles as many times as possible. I wasn't able to get this to always work depending on where the poison puddles landed, but it IS possible.It should take a little less than a minute for the first enemy to die.

Because every late game run requires you to play the full 10 minutes, I recommend alternating between this and the Rock minigame so they can scale up together.

The hardest minigame to scale. You only need 4 bonus unlocks, but it's significantly slower without the ability to explode the entire screen.

Scaling: The number of diamonds, each diamond gives 5% when hit with bonus balls. Other multipliers matter less and less the later you get.

Early Set-up: Rush for Multiplier as it scales fastest early game, then SSP, then bombs. Don't bother with the bonus balls until you get diamonds. Unlock the extra layers as soon as possible and get their "Earlier upgrades" as well. After you have a decent amount of bombs, try to get super stamina potions with a decent base of stamina for effectively unlimited stamina.

Mid Game: Unlock all the levels, then focus on trying to get the highest multiplier string possible and finishing with a SSP. Use bombs to avoid digging when you are about to lose a multiplier or to get more bombs.

Late Game: Explode everything, but leave the last layer. Use any SSPs that are not queens until you roll a queen. At the last layer, look for a bomb and explode it with the SSP multiplier and the big multiplier you got from exploding everything. If there is no bomb, reset or manually set a bomb and use SSP on the manually set bomb. Then try and hit as many diamonds as possible with the bonus balls.

You need about 182 More Diamonds to hit the critical mass of diamonds necessary to get 1 Decillion Rocks easily (minimal steering). There is a heavy luck component to this based on diamond density and your ability to steer the bonus balls. Unlike the Crystal minigame, this one requires more on waiting for Auto Gather so you can get the next More Diamond upgrade so you can slightly increase the scaling for the next dig. I recommend alternating between this one and the Crystal Minigame.

Easiest way is with Tankston Meat Shield with Champion's Cheese, Healing Hood, Spike Armor in EVIL mode.

Do NOT give any armor or equip the bleed ring. You should randomly get this at some point by autobattling in Evil Mode, but look for the demons in Fight 18 in one of the 50 FIghting Pits. If you just spam defend with everyone and heal with Tankston Skill/Special, eventually one of them will hit Tankston for 200+ damage.

You could use Ticktock to prevent the enemies from taking turns (and thus dying to status effects) while using Chop/Nyx to apply a ton of status effects, or use Cleanse to multiply reflect a ton of status effects.

Or you could just wait until the Ending and use Chop/Nyx skills and special repeatedly.

Easiest in Evil Mode, where you can also equip 4 items, but definitely doable in Standard.

Most should be able to beat with the tactics described in the first section. If you want, you can fish out more books from the ice fishing minigame and stack more health/speed to make it easier.