Toxrill ***** Counter Copy Bug
Delina, Wild Mage interaction with Toxrill, The Corrosive seems bugged.
Toxrill and Delina both in play and move to combat phase; Attack with Delina and target Toxrill as a creature to copy as a token tapped and attacking. If resolved (and especially apparent if the D20 roll results in >14 to create multiple token copies) The Toxrill Tokens on ETB will apply ***** Counters on opponent creatures During That Combat Phase rather than "The beginning of each end step".
MTG Arena on PC
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[Deleted User] commented
Having multiple copies of Toxrill on the field will cause creatures with ***** Counters on them to now get -X/-X, which would be the number of ***** Counters multiplied by the number of Toxrills in play. Are you sure extra counters were being placed?