Response

Choose target instant or sorcery spell, then roll d12. Put the result onto the stack targeting that spell.

1SpelljackSpelljack
2Mana ShockMana Shock deals X damage to you, where X is the converted mana cost of target spell. Add X colorless mana to your mana pool.
3ForkFork
4ScatterChoose new targets at random for target spell.
5Wild RicochetWild Ricochet
6Mana SinkCounter target spell. At the beginning of your next main phase, pay X, where X is that spell's converted mana cost. If you don't, that spell's controller may put a copy of that spell onto the stack.
7Parallectric FeedbackParallectric Feedback
8Tibalt's TrickeryTibalt's Trickery
9SpellshiftSpellshift
10DuplicateTarget spell's controller puts a copy of that spell onto the stack.
11Sudden SubstitutionSudden Substitution
12DelayDelay
13Mages' ContestMages' Contest
14Invert PolarityInvert Polarity
15Access DeniedAccess Denied
16AethersnatchAethersnatch
17Arcane DenialArcane Denial
18Busted!Busted!
19CounterlashCounterlash
20Dash HopesDash Hopes