Catching every Rock

Verified against the spelunky.ai port v0.1.10 on 28 October 2026.

A Rock moving fast across the player costs him 2 hearts and stuns him, unless he wears the Pitcher's Mitt with empty hands, when he catches it. The catch is written for the object rather than the Rock, so it catches all of them.

Wearing a Pitcher's Mitt, the player throws a Rock at a wall and catches it on the rebound. The two Rocks lying on the floor jump into his hands with it, and when he throws, all three fly together ^[1].

The player's step finds the Rock nearest him among those touching him, and if it's moving faster than 4 pixels a step and isn't one he's just thrown, either hurts him or, with the Mitt, catches it ^[2]:

        if (global.hasMitt and !holdItem)
        {
            holdItem = oRock;
            holdItem.held = true;
            pickupItemType = holdItem.type;
        }

The Rock it found is obj, but the catch puts oRock in his hands: the object, not the instance. In GameMaker, setting a variable on an object sets it on every instance of it ^[3], so holdItem.held = true makes every Rock that's awake held, and the shared item code puts each held item in the player's hands ^[4]. The throw then sets the speed of holdItem, every Rock again, so they all leave together ^{[5] [6]}.

Wear the Mitt, with empty hands, and let a fast Rock hit the player once its few safe steps after a throw are over: his own Rock coming back off a wall, or one an explosion throws. Any other Rock near the screen comes to his hands with it. The replay of the clip's staged scene pins it: a Rock thrown at a pillar comes back at 7 pixels a step and is caught, and all three Rocks in the room are held until he throws them, all at the same speed ^[7].

The spelunky.ai port reproduces it exactly: it's in docs/quirks.md's list of the 1.1 source's bugs ^[6], and the oracle's fingerprint of the replay pins every Rock's flight. No option turns it off.