Funko's Mystery Minis collection consists of a selection of small vinyl figures (hence "mini") that are approximately 2.5 inches (6.35cm) tall, widths vary from figure to figure. Mystery Minis are bought in blind boxes  and so the buyer does not know which variation of the figure they are buying until they have paid for and opened the box.
Most Funko Mystery Minis series contain 12-17 different characters/variations of a figure (see Portal Turret Mystery Minis), some (such as The Walking Dead Mystery Minis) also containing much rarer figures that have either a variation of a previous figure such as a glow-in-the-dark finish or a completely different design overall.
The Mystery Minis collection is a fun but costly way to collect Funko vinyl figures. Unlike Pop! Vinyl figures, the buyer does not know what they are buying and therefore to complete their collection they must keep buying many bind boxes, with most people finishing up with many duplicates. These duplicate figures (figures which somebody already has in their collection) are often sold on websites such as eBay or traded for figures which the buyer does not already have in their collection.
RRP: $6.99/$9.99 USD or £6.99/£7.99 GBP (price varies by brand/characters etc)