click setup then play. the WC diffs by tile id and runs slide -> merge-pop -> spawn-in. switching scenarios resets ids so consumed tiles fade in place (no merge target).
spawn -- two tiles appear on an empty board
slide -- one tile travels across an empty row
merge -- two 2s slide together, double, pop
chain -- four 2s in a row become two 4s
move -- slide-left over a populated board: one merge, three pure slides, one spawn. all three phases on one transition.
big board -- palette + font-size ramp across all tile values