Determined Seven

Determined seven is a series of bosses knowed as "HardBosses" these bosses are very known by they difficulty

Bosses:

Fatal error (2 phases)

Dust Sans (Gives Flame Eye, Walk in a diagonal way to have a chance of dodging bone circles, Dust also have 5 phases. There are three ways to kill Dust Sans if you are good in dodging use Scythe [Although not recommended], if want to play safe use Gaster Hand, Use Mew Mew staff to have a consistent damage also good for playing safe [Recommended way].)

Fresh Sans & Horror sans (Fresh Sans attacks with Tattletail that can sometimes be small and large, Uses disco balls that deals a lot of damage below 150 hp and summon Parasite after death, To continue, let Parasite hit you then dialogue starts. For Horror Sans, He throws axe at you so it is advisable to run in circles also attacks with spike zone. There are 2 phases, Below 150 Horror Sans become enraged and becomes faster and a faster axe throw, Horror sans can also spawn more Spike zones each time)

Cross Chara (Cross Chara is sometimes long because of how hard it is to hit him, It is recommended to hit him once he is running towards you becareful of the dash, Cross chara can heal himself if you get hit by the dash)

Overwrite Chara (A hard mode version of Cross Chara, Drops X Blade)

[How to fight Overwrite Chara: Press the OVERWRITE button in the picture of Cross Chara's Yellow door, Can also be fought by letting Cross Chara dash into you until he gets to 1000 hp]

Nightmare (Enrage mode below 50 hp, and it is recommended to use Flame Eye [If you have Mew Mew Staff it can be a way to deal extra damage] to have a better chance for killing it.)

Red (Original Undertale Concept of battle And 2 phases and it is recommended to get hush puppies [with Pies (1-2) if you can] because the fight is very hard and can usually kill you if you're not carrying foods.)

(Killing everyone without dying and leaving gives you a checkpoint and D7 pass.)

Alphys & Ness (Alphys is a survival boss that is defeated at a certain time, Ness appears after beating Alphys, Ness uses Flames, thunder zap, and freeze. It is not recommended to fight Ness by melee. Using flame eye [and mewmew staff or gaster hand] is recommended)

Dio Duck (2 phases, gives soul sword)

Also, there is a secret buffed dust sans behind dust sans called Hyper Dust Sans. He drops the Flame Eye too. (it is in mirrored D7 now.)