When shooting a trident enchanted with riptide towards the ground, you temporarily glitch through the blocks revealing caves and dungeons. Only tried on MCPE version 1.16.40 on singleplayer. I tried on many different world and ended up with same results. Will try on different device and give my results.
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We're tracking this issue in MCPE-64010, so this ticket is being resolved and linked as a duplicate.
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