Variant Mode
Variant Mode is a special feature smaller to Assist Mode and becomes a toggleable setting after finishing 8C. Its main purpose is allowing players to modify parts of the game to make it more challenging. Variant Mode also lets you use the "assists" you can find in Assist Mode. A save File currently using Variant Mode will have a banner on the save file select menu.
Variants
These are all of the values you can change to modify gameplay using Variant Mode
Game Speed
Allows you to change the games speed to any multiple of 10 between 50-160%. Having the game speed set lower can give you more time to react to what's happening. Well setting the speed high makes gameplay significantly more difficult.
Mirror Mode
Flips the whole map to appear mirrored. This however does not effect the games controls. some particle effects like the points you get from strawberry's are also flipped.
360 Dashing
Allows the player to dash at any angle instead of the eight directions normally. This can help when trying to pull of a specific move, and in some cases make tricks much easier. 360 dashing mainly effects people who play with controllers, and does change keyboard controls.
Invisible Motion
When moving Madeline will become completely invisible, making it hard to keep track of where you are.
No Grabbing
Completely Disables Madeline's grab move making many sections harder and possibly requiring neutral jumps. Despite that you can still perform wall jumps just fine.
Low Friction
All surfaces you can stand on become more "slippery". Causing you to retain more momentum
Super Dashing
Causes all Dash's last substantially, making smaller more precise movement far more difficult. However In some cases having longer dash's can open up sequence breaks. Allowing you to skip entire rooms.
Hiccups
Causes Madeline to hiccup every few seconds, bouncing you into the air slightly. they also make you fall off of walls. if you are able to time it right you can stay in the air for a few extra frames using a hiccup.
Other Self
Causes Madeline to change in appearance to look like badeline. This is a completely cosmetic and doesn't affect gameplay.
Assists
Enabling Variant Mode also allows the player to use the same "assists" found in Assist Mode