I have lost an enormous amount of games because of the following:
(Background info, when Derevi is played on an opponents land, it will show a box: Want to tap/untap land? Yes/NO)
When Derevi comes into play and targets something (for example an opponents land). They will tap it and play a removal spell on Derevi.
Derevi is destroyed/exiled and then a HUGE arrow pops up towards the land and a box pops up with a question and then YES/NO.
Obviously without thinking you click no, no i do not want to untap my opponents land, highlighted with that enormous arrow pointed at it.
So i click no. And Derevi stays in the graveyard/exile zone and it prompts me to untap the opponents land with a YES/NO.
See what happened there?
This has gotten me so many times.. litteraly dozens