A summon is a saga creature, so it works exactly like a saga: Once you reach the final chapter, and its triggered ability resolves, you have to sacrifice the saga
The only really uncertain part of the reconstruction is that Latios and Slowpoke - possibly due to someting about their position on the sheet - seem to have a tendency to get flipped around, so both appear first in the sequence twice
Of course, its impact is seen well outside of EDH, with Legacy decks and Vintage Cubes built around its existence
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Every 33 packs you should nab that card (Temporal Trespass) and the others will be every 16 packs, making them a much more common drop than the traditional foils
PlayRavnica Three Guilds of Ravnica packs