Parcly and Tori Taxel, after having wished genies' chess into existence and played around with it – noticing the link to Zarankiewicz's problem and getting an OEIS entry published in the process – decided to play Magic: The Gathering afterwards. While teaching each other the rules, however, they reached a position where Tori had exactly 161 cards on her side of the battlefield.
It was now Parcly's turn, and she played a card called Marijn's Bluff*, which read
Your opponent indexes the cards in their side of the battlefield starting from 1 as they like. You win the game if in this ordering there are $x$ and $y$ such that cards $x,y,x+y$ all exist and are all the same colour; $x$ may equal $y$ and multi-colour/colourless cards may be taken as any single colour.
Without resorting to other MtG cards/rules, and bearing in mind that the game has five colours, must Tori lose no matter what her 161 cards are?
*Obviously Parcly had magically written her own text onto this card; MtG and Parcly's universe of MLPFIM are both owned by Hasbro.