A much more detailed version of this guide is available here:

https://medievil.wiki/w/Speedrunning:MediEvil_(1998)_Any%25

Info

Read 'Basic glitches' first to learn the main glitches.
Follow the [SETUP] guides to have the correct emulator and autofire for the speedglitch

The Hilltop Mausoleum

1 second save - break spikes with club. Flipping the camera at green rune area is not faster
QUIT OUT
See video for timing

Return to the Graveyard

Boss - UPRIGHT a little bit, jump hit, mash X as fast as you can
Open pause menu when gate is open enough to be a doorway
Close pause menu after 1 or 2 seconds

The Enchanted Earth

LOOP (Easy)

DPAD
Wait until pillar points are very slight past halfway between topleft and bottom right cloud
Close invent at blue wall (CRUCIAL)
RIGHT
UPRIGHT when you face upright

LOOP (Hard) (7s faster)

See video for reference
DPAD
Wait until the platform covers good amount of the right cloud
Dash UP off
Close invent quickly
Use your timer to count to 6 from when you pass the ground, include the current second
Hit ground = 1... to 6.5
Desynced = 1... to 6
You should land 11 seconds after ground disappears

Pools of the Ancient Dead

Fast as possible invent glitch
Use helmet when you see red skull
Straight line from corner of platform

The Lake

UPRIGHT dash jump at start
Cut the corner on left turn
Smallest first jump on exit

The Crystal Caves

LOOP

ANALOG then DPAD
Loop from RIGHT of spawn
Close invent on 4th arrow flash
1 dash UPRIGHT
Switch to DPAD UPRIGHT
When you see the exit ledge stabilise, DOWN
When the screen shakes, RIGHT to straighten the crystal platform
UP
Go a little RIGHT of straight (Tap UPRIGHT UP etc) to hit exit directly

The Gallows Gauntlet

RUNE SMUGGLE
Best setup seems to be:
2 memory cards enabled
Existing save file on memory card 1
As soon as save successful appears you can quit (NOT BEFORE)

FIRST CLIP (INCONSISTENT):
DPAD
Lure mummy
Turn camera around
Hold RIGHT into corner of gate
Keep jumping at full height. Dashes don't help
The mummy will push you through (this is the inconsistency)
Tapping R2 once if you're not getting it can make it work

KNOCKBACK THROUGH GATE
Horizontal gate
Direction feels like DOWNRIGHT, input display says it's more RIGHT
Make sure your analog flick is PROPER, that's the key
UPRIGHT after stepping on pressure plate

DGS
ANALOG
Hold UPLEFT, get stuck at invisible wall
SQUARE, 2 frames later TRIANGLE CIRCLE + DOWN (Slightly DOWNRIGHT

Do not rush the jump. Run into the wall for a moment and focus on the inputs you must press
If you fail getting stuck on invisible wall, run away, stop, and go back to the wall with UPLEFT again

The Haunted Ruins

LOOP 1
Run straight UP with DPAD at start of level to arrive in exact spot
Analog then DPAD
When you run off it must be EXACTLY straight, no curving
UP - mash 9 dashes (Dash as fast as possible. The speed that the dashes come through is key)
Stumbling on edge does not affect results
If you miss the halfloop, hold UPLEFT

LOOP 2 (Old method)
Stumble up, then stumble right
Analog then DPAD
Jump off right
9 DOwN
when castle vanishes
1 LEFT (crucial to hold LEFT for the proper amount of time)
5 UPLEFT

LOOP 2 (New method)
Dash into wall
Sidestep up, stumble
Invent ANALOG run off
9 DOWN
Instantly when you see the castle:
2 LEFT, switch to UPLEFT at correct time and continue to spam
Slight taps LEFT can get you to land on the good mountain (be careful)

Movement after lever before catapult is biased towards left

The Ghost Ship

LOOP
Dash UPRIGHT at start of level to not hit wall, switch to DPAD
Run DOWNRIGHT to pillar
DPAD
Dash jump off UPRIGHT
RIGHT when railing touches top of screen = guaranteed direct land on exit
On second star flash, use timer to count and wait 2 seconds (see video)
Hold DOWNRIGHT for 7 and a bit seconds
Hold RIGHT

The Time Device

LOOP
Hold select before level starts
Dash jump off RIGHT
ANALOG
Hold UPRIGHT until track stabilises
Hold DOWNLEFT to straighten the track
QUIT OUT (1s timesave)
Use music as reference (see video) - 1 TWO! 3 1 (THREE is safer)
Open pause and quit

Zarok's Lair

Hold DOWNRIGHT after room entry
You do not have to take the shield

Soldier despawn
See video reference
Inventory glitch into cutscene
Close invent very quickly at correct time
Best method seems to be stand and hope the fight goes well
The crucial thing to get a fast fight is the closing of invent timing and speed during the cutscene
Cross other half of room to spawn soldiers ONLY after battle is won

Kardok skip
Stand next to last soldier
Camera locks on to you, mash select (about 8 times)
50% chance of either outcome:
If he's behind door = success, close invent as late as possible in the cutscene
Empty door = fail, cancel invent immediately
Run LEFT
Kardok moves in a repeating diagonal pattern

If you failed skip:
Stand against the wall to help with accuracy (move away before his 7th swing or he runs away)
Step forward to him and keep tapping up to stay in contact
Keep your aim exactly focused on him

Zarok
13 second zarok is the best possible
No shield use
Keep running away and stopping to bait vulnerability
Don't get too close to him, don't go too far away
Keep the camera straight
Focus on mashing attacks and expect him to go vulnerable
Control the fight