Deadly nightshade
A highly poisonous nightshade containing tropane alkaloids.
Aconitum napellus
Русское название: Борец синий, аконит
A striking blue-violet garden and mountain flower containing potent toxic alkaloids. Ingestion can severely affect heart and nervous-system function. It is unsuitable for any homemade remedy.

Do not use photographs or online summaries to identify wild plants for eating or medicinal use. Some poisonous plants resemble edible species and even handling certain species can cause harm. If poisoning is suspected, contact your local poison service or urgent medical care. Do not wait for symptoms.
Poison Control: poisonous plants (US) ↗Mountain regions of Europe
Moist mountain meadows and gardens
Images and brief descriptions are for learning, not for reliably identifying a specimen. Take particular care with poisonous plants and mushrooms.
Identification is never guaranteed by a photo. Scientific names are used to reduce confusion between local names.