How can you create a combo with Rootha, Mercurial Artist, Twincast?
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[START OF COMBO]This combo can be formed with Rootha, Mercurial Artist, Twincast

Color identity: UR
Mana cost: {2}{U}{U}
Steps:
  1. Cast an instant or sorcery spell, or wait for an opponent to cast one.
  2. Holding priority, cast Twincast by paying {U}{U}, targeting the spell.
  3. Activate Rootha by paying {2} and returning it to your hand, copying Twincast, with the copy targeting the original Twincast.
  4. Resolve the copy of Twincast, copying Twincast, targeting the original Twincast.
  5. Repeat step 4.[END OF COMBO STEPS]

Result:
  - Infinite magecraft triggers[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Rootha, Mercurial Artist must be on the battlefield
  - Twincast must be in your hand
[END OF COMBO PREREQUISITES]
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