This post is from a low-reputation account and contains an unverified outbound link. Be cautious before clicking external links.
https://splinterlands.com?p=battle&id=sl_0860b8899dbe4c0f517724dcde7fae3b&ref=kingfish12
Here is another replay that the fatigue damage mechanic came into play. It does seem like the rule is always after round 20 all cards will begin to take damage directly to their health. This time luckily I had more health than the remainder of the opponent's cards combined so I could just outlast the damage. This mechanic adds an interesting twist and can be used in your next strategy. Finding cards that have a lot of health and/or the "tank heal" ability could be placed at the end of your deck and possibly last longer than 20 rounds.