This card is the epitome of what tournament
players refer to as a glass cannon. If you have
the right hand, it can kill in one attack. If
you don't, it's not even clearly ahead of cards
that are often considered sub-par (I've been
taking a second look at Mage-Ring Bully now that
the last core set is leaving Standard). But red
is finally embracing its identity as a color of
instants and sorceries, and there are a
surprising number of "right hands", from the
obvious Lightning Bolt and Assault Strobe to
more off-the-wall choices like Tainted Strike.
Kiln Fiend is, in the right deck, brutal. +3/+0
is a massive bonus to be attached to each
instant and sorcery, meaning that the little
fire dog can burninate your opponents in record
time. In theory, you can power out a turn 2 or 3
kill with Kiln Fiend! (It involves Assault
Strobe and the Phyrexian mana spells, especially
Mutagenic Growth.)
It's still a fragile card that requires you to
be focusing in on burning your opponent to
death, but it makes for a good finisher in
spellslinger-type decks. It's especially lethal
in Pauper, and it's even good enough to see
fringe Modern play. Just make note that it asks
a lot of you in order to make it work well.