Manahive

Equivalent cards in Izzet (blue-red) that care about casting your second spell each turn include:

• Goblin Electromancer (UR — not exact, but helps casting multiples)
• Stormchaser Drake (U — triggers on casting spells that target it)
• Saheeli, Sublime Artificer (UR — makes a Servo for each noncreature spell cast)
• Young Pyromancer (R — creates tokens on instant or sorcery cast)
• Murmuring Mystic (U — makes tokens on instant or sorcery cast)

Reason: Original card triggers on second spell; others reward you for casting multiple or specific types of spells. Closest synergy is Saheeli, Sublime Artificer and Young Pyromancer.