Ruby, Daring Tracker - Intelligence

Ruby is strongest when she comes down early, immediately makes mana, turns that mana into land ramp, and then attacks only after a power-4 creature is already in play. The cards to check first are durable ramp, power-based draw, cascade payoffs, and the Bard Class combo package.

Ruby has haste, so she can attack and use her tap ability as soon as she comes under your control.

Ruby's attack trigger checks whether you control a creature with power 4 or greater as Ruby is declared attacking.

Ruby counts herself only if her power is already 4 or greater before attackers are declared.

Removing or shrinking the qualifying power-4 creature after the ability triggers does not stop the +2/+2 bonus.

The attack trigger resolves before blockers are declared.

Extra combat phases can trigger Ruby again if she attacks again and the power-4 condition is true.

Ruby's mana ability is a mana ability and does not use the stack.

Commander tax can break Bard Class loops unless the cost reduction and return-to-hand sequence account for it.

Bard Class level 2 reduces the cost of legendary spells; level 3 adds the exile-and-play permission during the loop.

Agatha of the Vile Cauldron reduces activated abilities of creatures you control based on Agatha's power, but it does not make illegal off-color cards legal.

Kogla and Temur Sabertooth variants require separate bounce costs and board states.

Cascade deckbuilding can constrain low-cost interaction because cascade cares about mana value.

Lead on Ruby, use her mana immediately, and turn that start into land ramp rather than fragile mana creatures only.

Use Ruby to reach cascade and discover spells ahead of curve, then chain into pressure or draw.

Use Ruby as the early bridge into large creatures that turn on her attack trigger and win through combat.

Use Bard Class cost reduction with Ruby's mana and a legal activated-ability reducer or bounce engine.