This Ability effect may be in need of research. Reason:If a Pokémon holds a Utility Umbrella, is it unaffected by its ally's Flower Gift? Is Hydro Steam affected by the Utility Umbrella? You can discuss this on the talk page.
The holder's Abilities and self-targeting moves behave as if there was no rain or sunlight present (with the exceptions of Protosynthesis and Orichalcum Pulse). For example, if the holder has Chlorophyll or uses Growth or Synthesis in harsh sunlight, it will not have its speed doubled, boost stats by only 1 stage, and heal only half of its HP, respectively.
Water-type and Fire-type moves targeted at the holder will not have their power decreased or increased in rain or sun. Moves with a different accuracy in rain or sun, such as Thunder, have their normal accuracy when targeted at the holder. Conversely, these weather effects are applied as normal to the holder's moves.
In rain or harsh sunlight, Solar Beam's number of turns to charge and power is unaffected by weather if used by a Pokémon holding the Utility Umbrella. During rain or harsh sunlight, the holder's Weather Ball will be Normal-type and its power will not be doubled (as if no weather was present). However, weather effects are applied as normal to Solar Beam and Weather Ball targeted at the holder.
A Pokémon holding the Utility Umbrella can be frozen in harsh sunlight.
Overcast Form Cherrim holding a Utility Umbrella cannot change to Sunshine Form. If a Sunshine Form Cherrim gains the Utility Umbrella (through a move such as Trick), it will immediately change to Overcast Form. Likewise, a Cherrim losing the Utility Umbrella in the sun will immediately change to Sunshine Form.
Outside of battle
The Utility Umbrella has no effect outside of battle, so Sliggoo is still able to evolve while holding the Utility Umbrella.