Edit: As of 19-Nov-2024 the game was patched with online features. This update comes with 3 achievements that area easily obtainable (even playing solo with just the multiplayer lag)

Getting 100% was... hours and hours of addictive, frustrating game-play

approximate amount of time to 100%: 200+ Hours (likely much more)
Estimated achievement difficulty: 10/10
Minimum number of playthroughs needed: Millions :) Jokes aside 500 or so.
Multiplayer achievements: No.
Missable achievements: No.
Point of no return: No.
Grinding Achievements: Yes, Run after run after run after...
DLC-Only achievements: Yes. 3 DLC packs each with hundreds of achievements.
Time-gated achievements: No, but participation in dailies awards multiple achievements.
Speed-run achievements: No.
RNG-achievements: No.

Notes:
* Once per day Disable all Mods and start a daily run... At worst you just die in the first room for 31 days, that's ok ...at best you win 7 times total or 5 in a row. Since all of these have achievements, i recommend you start this one early.
* Unlocking characters has varied and obscure requirements, recommend using a guide.
* Most achievements unlock when beating each of the bosses with each of the characters for the first time.
* Achievements are disabled while mods are active... UNTIL you beat mom for the first time with no mods... Mods make this game extremely easy so in theory it just becomes a couple of hours grind.

So yeah... The game is kinda addicting, in that Vampire Survivors way... Tho at I could swear the game is trolling you at times.
Overall recommened.

Edit: As of 19-Nov-2024 the game was patched with online features. This update comes with 3 achievements that area easily obtainable (even playing solo with just the multiplayer lag) Getting 100% was... hours and hours of addictive, frustrating game-play approximate amount of time to 100%: 200+ Hours (likely much more) Estimated achievement difficulty: 10/10 Minimum number of playthroughs needed: Millions :) Jokes aside 500 or so. Multiplayer achievements: No. Missable achievements: No. Point of no return: No. Grinding Achievements: Yes, Run after run after run after... DLC-Only achievements: Yes. 3 DLC packs each with hundreds of achievements. Time-gated achievements: No, but participation in dailies awards multiple achievements. Speed-run achievements: No. RNG-achievements: No. Notes: * Once per day Disable all Mods and start a daily run... At worst you just die in the first room for 31 days, that's ok ...at best you win 7 times total or 5 in a row. Since all of these have achievements, i recommend you start this one early. * Unlocking characters has varied and obscure requirements, recommend using a guide. * Most achievements unlock when beating each of the bosses with each of the characters for the first time. * Achievements are disabled while mods are active... UNTIL you beat mom for the first time with no mods... Mods make this game extremely easy so in theory it just becomes a couple of hours grind. So yeah... The game is kinda addicting, in that Vampire Survivors way... Tho at I could swear the game is trolling you at times. Overall recommened.