What is the principle behind this deck, and why play it?

• Prepare Biting Sun, then activate Solar spells under Zenith.
• Learn to master the Zenith status and take advantage of it.

Why the Lion?

• Component for Biting Sun.
• At the start of the game, it can inflict damage on the opponent for little cost, giving you time to prepare Biting Sun.

What cards could be suggested?

• Defense: Iron Will to protect your many permanents, Dazzle for little investment, Stunning Thunder to gain 1 turn.
• Damage: Sekhmet’s Rancor to simplify Zenith, Solar Explosion only when combined with Zenith Ritual + an effective discard method.
• Draw: Acceleration, Flash of Inspiration, Radiant Light.
• Utility: Animal Recall because your Lion will end up exiled, Stellar Fractal to recover certain spells or simplify Solar Invocation, Adaptation and Fiery Breath for your Animal, Sun Catalyst to simplify the casting of your Solar spells as a replacement for Biting Sun (see if the damage would then be sufficient).

Important: a variant with Earthquake and more Tornado to take advantage of Solar Eruption is viable.