It's a Quick-Play Spell, so you can use it preemptively or reactively
Saber Reflection X SPELL Quick-Play When you take battle or effect damage while you control an "X-Saber" monster: Gain LP equal to the damage you took, and if you do, inflict the same amount of damage to your opponent, then you can add 1 "Saber" Spell/Trap Card or "Gottoms" card from your Deck to your hand
These cards are included here so that you can use the starting hand and decks described on the back of each of the four prologue investigators, even if you do not own that expansion
In Magic, if you are looking to build a Chocobo Commander deck, then Choco, Seeker of Paradise is the go-to Commander
Mirror Force Launcher X TRAP Continuous Once per turn, during your Main Phase: You can discard 1 monster