Whenever you cast an instant or sorcery spell, choose one that hasn't been chosen —
• You may tap or untap target permanent.
• Gandalf deals 3 damage to each opponent.
• Copy target instant or sorcery spell you control. You may choose new targets for the copy.
• Put Gandalf on top of its owner's library.
Gandalf the Grey is an Izzet spellslinger engine that turns every instant and sorcery into incremental value. Each turn cycle you cast cheap cantrips, removal, and burn while picking off the modal menu — untapping a key permanent, draining 3 to each opponent, or copying your best spell. You chain spells with cost reducers and rituals to reset the menu and snowball into a lethal copied burn spell or storm-style finish.
Free spell copy on every cast effectively doubles your best instant/sorcery
Repeatable 3-to-each-opponent burn gives a built-in clock without needing creatures
Untap mode enables fast-mana and big-mana plays (untap a rock or land tapped for storage)
Deep, well-supported color pair (Izzet) loaded with cantrips and copy synergies
Resilient — the library-top mode lets you reset and reuse him while dodging some removal
The four modes only reset once Gandalf returns or is recast, so a single cast gives you one mode
Spell-light or flooded draws leave the engine idle
Five-mana commander that does little without a stocked hand of spells
Vulnerable to graveyard hate and stax that taxes noncreature spells (Rule of Law effects)
Removal-heavy metas can keep him off the battlefield, shutting off triggers entirely