Astigmatism's body basically consists of a large ball and four spiked limbs. The ball is accompanied by two "horns" on each side. When idle, a large eye can be seen on the ball also with three eyelashes. However, it changes from this sprite to another sprite where the eye hollow is changed with a smile. When having its eye closed, the two side- eyelashes become Astigmatism's eyes, while the middle one simply becomes a marking.
Astigmatism's attacks are similar to those of Loox's.
- Astigmatism summons orbs initially traveling diagonally up/down that bounce off the edge of the box once, which then travel vertically/horizontally straight the opposite direction it originally came from. Its velocity increases the longer the orb does not touch a wall, which resets the speed.
- Astigmatism summons groups of 3-orb entities from the right that travel to the left while spinning around clockwise or counter-clockwise.
- To spare this monster, the protagonist must wait a turn to read what it wants them to do; it will say either "Pick on me" or "Don't pick on me" before attacking. Taking the appropriate action will allow Astigmatism to be spared.
- Challenging an Astigmatism while other enemies are fighting will instantly make said enemies sparable.
- ...Pick on me. [Neutral]
- ...Don't pick on me. [Neutral]
- You've seen enough. [Neutral]
- Take your last look [Neutral]
- That takes guts. [Neutral]
- You've pushed your luck. [Neutral]
- That's right! [Obey Instructions, if Pick On]
- Finally someone gets it. [Obey Instructions, if Don't Pick On]
- What are you so afraid of? [Disobey Instructions, if it wants to be Picked On]
- How dare you. [Disobey Instructions, if it doesn't want to be Picked On]
- You dare defy me? [Challenge]
- This relentless bully ALWAYS gets its way. [Check]
- Astigmatism drew near. [Encounter]
- Eyes appeared from the shadows. [Encounter with other Astigmatism]
- Final Froggit and Astigmatism appeared. [Encounter with Final Froggit]
- Whimsalot and Astigmatism appeared. [Encounter with Whimsalot]
- What a nightmare! [Encounter with Final Froggit and Whimsalot]
- That doesn't seem correct. [Encounter with Final Froggit in Hard Mode]
- Not only potatoes have eyes. [Encounter with Parsnik]
- Looks like a real party. [Encounter with Migospel and Moldessa]
- Astigmatism doesn't care about fighting anymore. [Meeting spare conditions]
- Astigmatism gazes through your soul. [Neutral]
- Astigmatism gives you a hypnotizing glare. [Neutral]
- Smells like glasses. [Neutral]
- Astigmatism clicks its teeth. [Neutral]
- Astigmatism has gone bloodshot. [Neutral]
- You stand up to Astigmatism. [Challenge]
- You pick on Astigmatism. [Pick On]
- You don't pick on Astigmatism. [Don't Pick On]
- Astigmatism is watering. [Low HP]
- Astigmatism shares its name with the optical defect itself, a visual condition that can cause blurry vision, squinting, eye strain, fatigue, or headaches. This might refer to the eye motif that Astigmatism shares with Loox, and also how Astigmatism is supposed to be more severe and powerful than Loox, since one's eye would hurt more if one had astigmatism.
- Reaper Bird, one of the Amalgamates, is composed of Astigmatism, in addition to Whimsalot and Final Froggit.
- In the code, challenging Astigmatism when it's spareable should make it say "You've pushed your luck," but in gameplay, it seems impossible to do it.
|Main Characters||Flowey • Toriel • Sans • Papyrus • Undyne • Alphys • Mettaton • Asgore Dreemurr • Frisk • Chara|
|Ruins Enemies||Dummy • Froggit • Whimsun • Moldsmal • Loox • Vegetoid • Migosp • Napstablook|
|Snowdin Enemies|| Snowdrake • Chilldrake • Ice Cap • Gyftrot • Doggo|
Dogamy and Dogaressa • Lesser Dog • Greater Dog • Jerry • Glyde
|Waterfall Enemies||Aaron • Moldbygg • Woshua • Temmie • Mad Dummy • Shyren|
|Hotland Enemies||Vulkin • Tsunderplane • Pyrope • Muffet • Royal Guards • So Sorry|
|CORE Enemies||Final Froggit • Whimsalot • Astigmatism • Madjick • Knight Knight|
|Amalgamates||Memoryhead • Endogeny • Reaper Bird • Lemon Bread • Snowdrake's Mother|
|Hard Mode-only enemies||Parsnik • Moldessa • Migospel|
|Vendors||Nice Cream Guy • Snowdin Shopkeeper • Gerson • Tem Shop • Bratty and Catty • Burgerpants|
|Other Characters|| NPCs • Monster Kid • Annoying Dog • River Person • Eight Humans • Asriel Dreemurr|
W. D. Gaster • Lost Souls