The rock rules are terrible, I would even say pathological. They are:

* The rock is worth twice the big blind

* 🎅 The player with the rock must post it as a straddle immediately regardless of position

* Action preflop always starts UTG 🎅 unless the rock is UTG in which case it starts +1

* If a player in the blinds has the rock, 🎅 it replaces their normal blind