These will transform after you fulfill some kind of condition on the card, usually either an activated ability (i.e., paying to exile Terra, Magical Adept) or triggered ability (i.e., having six permanents in the yard for Exdeath, Void Warlock at end of turn)
Garth One-Eye Leave it to the Modern Horizons sets to create commanders that play out like Alchemy cards
If an instant or sorcery card is put into your graveyard during your turn, you'll be able to cast it right away if it's legal to do so, before any player may attempt to remove that card from your graveyard
Note that this is damage, not just combat damage if you can string some rituals and buffs together with cards like Storm-Kiln Artist, Birgi, and Haze of Rage, you can convert that into a Chandras Ignition with little effort