Spend

only

black

and/or

red

mana

on

X.

Soul

Burn

deals

X

damage

to

any

target.

You

gain

life

equal

to

the

damage

dealt,

but

not

more

than

the

amount

of

spent

on

X,

the

player's

life

total

before

the

damage

was

dealt,

the

planeswalker's

loyalty

before

the

damage

was

dealt,

or

the

creature's

toughness.