The pawns unionize.

A dragon roosts upon the rook at H8. This quadruples its power.

(This would be represented by a dragon atop 4 rooks)

Third possible move:

Suddenly, out of no where, all of the pawns remove their old fashioned postbellum hoop dresses and switch their icons to more form fitting, slender getups, smoking cigarettes and demanding the right to vote all as they march from left to right to left to right in the middle of the board and burn copies of Little Women in protest of being treated as little better than property by their husbands, the bishops, knights and rooks.

Fourth possible move;

The black pawn at F7 attempts to move down two tiles, proclaiming he is executing an en passant maneuver.

This causes the very old chess board, which has seen quite a lot of chess games and hates nothing more than the misunderstanding of the en passant maneuver, to open up its great maw, declare that the pawn has 'activated his trap card', swallow the pawn into sheol/hades underneath the board, and from there belch forth the mighty white eyes blue dragon, which takes up 2x2 in the center of the grid, is allowed 3 moves per each set of a black move and a white move, and appears to be hostile toward both white and black units.

Pawn to D5, a move so shocking the rest of black's pawns get shocked emojis

Other possible move: The butterfly flaps its wings meekly, wasting a turn.

Elsewhere on the planet, 38 years in the future, a sentient alien species crashes the ship containing the last remnants of their wise and noble species due to an unexpected category 6 hurricane at their projected 'safe' landing zone.

Missingno updates to his more modern circle-with-question-mark sprite

Roadwork on E4, pawn wears a hard hat and hivis gear for OSHA compliance.

Rook at A8 starts to wear a bucket hat, gets into camping at music festivals and gets really into drugs. He becomes...the wook rook

An earthquake (boardquake?) occurs, causing every piece to slide 0.5 squares in a random direction

D5

The Black King decides to watch Ru Paul, amd then decides to dress, rather immaculately for a novice, in drag for the remainder of the game.

This causes the White Knight on B1 to jump down one and right 3 in an attempt to Milady the newly fabulous Black Queen, but his advances are useless as all of his proposals of merit, offers of faithfulness and boasts of great honor are shot down by the advanced air defense systems of the missile frigate to the Black Queen's rear, whose sailors have given up on the Great Game of Black vs White, for they have been enticed by the Fabulous Black Queen's ample and enticing bubble butt, adorned in an absolutely stunning combination of crimson velvet and ochre latex, accented by tantalizing, chromatically reflecting mauve lace stockings.

EDIT: jesus fucking christ what did i just write

Is the mobik cube allowed to be a piece

Rook at H8 is rookie of the year Victor Wembanyama.

Knight at B8 in order to counter Whites growing fabulousness transforms into Divine.

In the christmas spirit Nero Claudis sings "Padoru Padoru" at b4

OP’s cat flips the board. Game over.