NEXUS MENTALITY This is a super interesting card and probably the best combat trick in the deck
You would be modifying your deck list and removing a card in the middle of a match, and physically tearing up a card probably counts as marking it which is not permitted
Pokemon trading cards are known for their sturdy construction and durability
Five mana is slightly high, but in Treasure-based decks, you can generate five mana with ease
Mienshao basically has one move that can do something no matter what other cards you have in your deck, I would try and have a few Pokemon with free retreat costs in my deck, use that Pokemon for awhile and then when the defending Pokemon is close to getting knocked out, move Mienshao in there and use Meditate to knock it out, Mienshao's retreat cost is low so you could retreat it back the next turn
If these games go really slow, then some of these might be good at breaking those stalled boards, especially this Crystal