Hello,

In a recent game of MTG Arena, I controlled Serra's Emissary and had already chosen "creature" as the protected card type since the previous turn. On the opponent’s turn, they cast Ulamog, the Defiler, and its triggered ability targeted me and resolved, exiling half of my library.

According to rule 702.16b, a player with protection from creatures cannot be the target of abilities from sources with that type — in this case, Ulamog's cast trigger comes from a creature spell.

Therefore, this interaction should not have been legal, and Ulamog should not have been able to target me or exile my library.

Please investigate, as this appears to be a bug.

Thank you.