If this is under powered, you could always bump damage a little, or even add some other effect / side effect.
You could shorten the wording a bit:
"
: Discard a card to deal 2 damage to target and 1 to surrounding creatures."
That leaves one line if you wanted to add something else...
E.g.: "
: Discard a card to deal 2 damage to target and 1 to surrounding creatures. High cost cards increase damage."
or
"
: Discard a card to deal 2 damage to target and 1 to surrounding creatures. Draw a card "
or
"
: Discard a card to deal 2 damage to target and 1 to surrounding creatures. (x uses per turn)" - where X is some number that seems good.
or
"
: Discard a card to deal 2 damage to target and 1 to surrounding creatures. May stun targets "
The only issue I see here is that you would either need to make the discard effect random or the creature targeting random... Otherwise it would require 2 targets being picked.