Slaking's only obtainable ability is Truant, though you can alter this ability in battles, with there being two ways you can change Slaking's ability mid-battle.
- If you make contact with a Runerigus and Cofagrigus, Slaking's ability will be replaced with Mummy and/or Wandering Sprit.
- If a Pokemon uses Skill Swap on Slaking, their abilities will swap with each other. An example of this would be if a Starmie with Illuminate uses Skill Swap on Slaking, where Slaking's ability will change to Illuminate, while Starmie's ability will become Truant. A good candidate for this in double battles would be Stakataka, as you could give Slaking the ability Beast Boost.
Honorable mentions would be Neutralizing Gas and Gastro Acid. Neutralizing Gas is the signature ability of Galarian and Kantonian Weezing, while Gastro Acid is a move learnt by several different Pokemon. These both nullify the affects of Truant, but don't necessarily change Slaking's ability.
Unfortunately, all these methods aren't permanent, and end once a battle is won or you switch Slaking to a different Pokemon.
All abilities any Skill Swap Pokemon may have:
Synchronize
Inner Focus
Magic Guard
Trace
Healer
Aroma Veil
Competitive
Regenerator
Klutz
Levitate
Insomnia
Frisk
Cursed Body
Prankster
Telepathy
Analytic
Natural Cure
Serene Grace
Blaze
Magician
Heatproof
Heavy Metal
Compound Eyes
Tinted Lens
Unnerve
As One (Glastrier)
As One (Spectrier)
Clear Body
Sturdy
Mummy
Honey Gather
Shield Dust
Sweet Veil
Pressure
Magic Bounce
Swarm
Aftermath
Unburden
Flare Boost
Forewarn
Keen Eye
Own Tempo
Chlorophyll
Harvest
Steadfast
Justified
Pixilate
Shadow Tag
Early Bird
Sap Sipper
Pickup
Thick Fat
Gluttony
Anticipation
Magician
Dry Skin
Oblivious
Color Change
Protean
Multiscale
Hydration
Soundproof
Filter
Technician
Screen Cleaner
Ice Body
Tangled Feet
Water Compaction
Sand Veil
Overcoat
Wandering Spirit
Wonder Skin
Shell Armor
Hydration
Contrary
Beast Boost
Intimidate
Unaware
Simple
Cute Charm
Psychic Surge
Victory Star
Anticipation
...That should be all of them, these abilities aren't in any particular order, because I find that lists are lame!
