When it comes to describing something that's shimmering, it's important to have a variety of synonyms at your disposal to really capture the beauty and intricacy of the effect. Some alternative terms for "shimmeringly" might include "glitteringly", "sparklingly", "twinklingly", "gleamingly", or "flashingly". Each of these words conveys a different element of the shimmer - whether it's the gentle, twinkling glow of a distant star, the brilliant flash of sunlight on water, or the iridescent glow of gemstones and precious metals. By using these synonyms, you can create more nuanced and vivid descriptions that bring your writing to life.