Opening Obsidian Flames Single Blister Pack [Revavroom] returns about $4.35 in card value against its $17.60 price — roughly $0.25 back per dollar spent. On current prices, you lose money on average by opening it.
See every card and pull rate in Obsidian Flames
How expected value is calculated — card value only, from published pull rates and daily market prices.
Obsidian Flames Single Blister Pack [Revavroom] on TCGplayer