Phyrexian Slith trigger didn't work properly
I had Phyrexian Slith and Cursed Wombat under my control
The opponent had Faithful Watchdog under their control
I attacked and dealt damage to the opponent with Phyrexian Slith
Two triggers went to the stack, the Slith gained two +1/+1 counter (the second is from the Wombat)
But then I wanted to take a +1/+1 counter off of the Watchdog twice, but the only option I had was a Decline on the first trigger and the second one didnt even ask me anything
The expected result: I take off two counters of the Watchdog
I didnt make a screenshot, unfortunately
And I proceeded to the next game before I took logs (in attachment)

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BillyBobJoe2756#05502 commented
I had this same issue and it caused a significant disadvantage to me in the game as well. However, I dont think that the wombat trigger will remove counters.
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Djebedia#15016 commented
yes, that's true - in that case it should've removed one counter, however none were removed
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DAC169#34537 commented
"Whenever Etched Slith deals combat damage to a player, put a +1/+1 counter on it. When you do, you may remove a counter from another target permanent or opponent." This is all one ability, not two. It doesn't matter how many +1/+1 counters you place on Etched Slith or how you're putting them onto it. It will only remove one counter from another permanent or opponent when it deals combat damage to a player.