Ozolith and Quirion Beastcaller
When a player has The Ozolith and Quirion Beastcaller in play, and Quirion Beastcaller dies with +1/+1 counters on it, the following happens:
The player may move the counters to another creature (according to QB's card effect). At the same time, a copy of these counters will all be assigned to the Ozolith (per the Ozolith's card effect). This has the overall effect of doubling the +1/+1 counters available to the player.
This was observed playing Historic on PC.
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TysonNW#19991 commented
Ozolith, the Shattered Spire has the ability "If one of more +1/+1 counters would be put on an artifact or creature you control. that many plus +1/+1 counters are put on it instead." If I play it on one game, the next game I play that effect is still active.
In the second game with nothing on the board I play a Querion Beastcaller. The next turn I play any creature and instead of getting a +1/+1 counter, the Beastcaller gets 2 counters.