This is a very broad category, as almost any part of the card can be part of the theme
Incessant Onslaught has some pretty insane abilities to scale into a very heavy swing late game, making it a handy tech into certain decks
And the WOTC-era provenance gives the card vintage credibility that modern cards cannot replicate

Abigale, Eloquent First-Year Abigale, Poet Laureate Assembled Ensemble Bello, Bard of the Brambles Blazing Firesinger Bonebind Orator Campus Composer Chong and Lily, Nomads Composer of Spring Crime Novelist Draconic Muralists Elvish Bard Firbolg Flutist Flamebraider Gylwain, Casting Director Harmonized Trio Huatli, Poet of Unity Inspiring Bard Insufferable Balladeer Joraga Bard Kalain, Reclusive Painter Kitt Kanto, Mayhem Diva Korlessa, Scale Singer Leitmotif Composer Lotuslight Dancers Melancholic Poet Merry Bards Mockingbird Moku, Meandering Drummer Molten-Core Maestro Mutant Town Musicians Narci, Fable Singer One-Clown Band Orysa, Tide Choreographer Prismari Pianist Psemilla, Meletian Poet Raccoon Rallier Raucous Entertainer Rehearsed Debater Slimy Piper Songcrafter Mage Spellbinding Soprano Starfield Vocalist Stirring Bard Stirring Honormancer Stirring Hopesinger The Mary Janes The Wandering Minstrel Thistledown Players Three Dog, Galaxy News DJ Thunderdrum Soloist Tom Bombadil Totentanz, Swarm Piper Valor Singer Voice of Victory Wandering Musicians Wandering Troubadour Wandertale Mentor Whiskervale Forerunner Yisan, the Wanderer Bard Zaffai and the Tempests Zinnia, Valley's Voice

Notice the two monkeys allegedly copulating in the background