Quill, you're right Shower of Coals is amazing in Multiplayer (and limited too). In MP you will always have 3 targets and you will most likely have threshold too. One of the best MP burn spells ever.
I agree with Duel about Barbarian Ring in extended. Yes you are giving up a land for a 1R shock but, it IS colorless which makes a huge difference. It also has a Seal of Fire effect where the opponent always realizes all you burn spells now do X+2 damage. Plus it does produce red mana WITHOUT coming into play tapped making 4 in a deck a non-issue. Finally, its uncounterable, Force this baby.
Disadvantages:
Its a painland - Sligh really doesn't care about this, might hurt you 1 in 25 games.
Threshold - 4 cards in your opening hand are in the graveyard by turn 3, most games don't end on turn 4. If it does that means you've won, if it doesn't that's when the Ring is going to help.
Has to sac for its effect - How much mana does sligh really need?