I was playing my infamous cruelclaw/ulamogs deck on (I pad) and noticed that they had over 100 cards in their exile zone which should not be possible in a 100 card format (no alchemy cards were cast by either player). Here is the sequence of events:
I mulligan to 2 cards, my opponent mulligans to 6.
Turn one (Me): fabled passage, pass
Turn one (opponent): swamp, pass
Turn two (me): draws swamp, sac the passage for a mountain, play the swamp as land for turn, pass
Turn two (opponent): fabled passage of their own, sac it for a forest, pass
Turn three (me): arena of glory, exert arena of glory to give cruelclaw haste, attack with cruelclaw, cruelclaw ability resolves allowing me to cast ulamog the ceaseless hunger from exile for free by discarding a card, ulamog cast trigger resolves exiling both of my opponents lands, pass the turn
Turn three (opponent): mana confluence, pass
Turn four (me): attack with both cruelclaw and ulamog the ceaseless hunger, exiling the top 20 cards of the opponents deck, cruelclaw trigger resolves allowing me to cast hit the mother load for free by discarding a card, hit the mother load has me discover 10 which finds ulamog the defiler, ulamog the defiler cast trigger resolves exiling the top half of the opponents deck, pass the turn
Turn four (opponent): land, pass
Turn five (me): attack with all, ulamog the defiler anihillator 8 trigger resolves causing my opponent to sac both of their remaining lands, ulamog the ceaseless hunger trigger resolves causing my opponent to exile the top 20 cards in their deck (they now have 12 cards remaining in their deck) combat damage is dealt and my opponent dies.

You guys do a great job and magic wouldn’t be what it is without all of your hard work, I hope this helps