https://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=197536

Runeflare Trap 4RR
Instant - Trap
If an opponent drew three or more cards this turn, you may pay R rather than pay this spell's mana cost.
Runeflare Trap deals damage to target player equal to the number of cards in that player's hand.

This card's effect isn't enough to pay 6 mana for, so you need to be able to trigger the alternate cost in order to be able to get good value out of it. Unfortunately the condition isn't something that most opponents are going to trigger consistently so you would need to build your deck around it. Luckily there is a deck that can do that and wants this effect, Owling Mine! Sure it's not a very consistent deck, but this is one of the cards that makes it work. If you really want to play this card, do it in that deck.