GRE is easily replicated in the following conditions:

"Ojer Taq, Deepest Foundation" with "Helm of the Host" equipped
"Rabble Rousing" and "Adeline, Resplendant Cathar" on board

Attacking using the tokens created from all 4 triggers instantly procs GRE error code and game ends in draw, without fail. I have managed in some games to create nearly 1000 tokens in a turn but there does seem to be an upper limit on the power Adeline is allowed to have, as the GRE error is hit or miss without her on board. With her on board, it is guaranteed to GRE error.