Will casting Expansion // Explosion explosion work with Radiate in a way to deck out all my opponents in an edh game if there is enough creature tokens lol or will the part that mentions 1 target not allow this interaction.
For the purposes of Radiate, Explosion "targets only a single ... player" if the same player is targeted for Explosion's "any target" and "[t]arget player" requirements (C.R. 115.9b-c, 115.1a, 115.4). Thus, if you've cast Explosion and targeted the same player twice with it, you can target Explosion with Radiate so that when Radiate resolves (and Explosion is still a legal target of it), Explosion is copied for each other "player that spell could target" and "[e]ach copy targets a different one of those ... players" (C.R. 706.10, 706.10d, 608.2b). (Even though Explosion also "could target" a creature or a planeswalker, a copy of Explosion isn't created for each creature and each planeswalker this way, since Radiate requires that copy to target such a permanent and that permanent doesn't satisfy Explosion's "[t]arget player" requirement [C.R. 706.10d, 115.1a, 115.4].)
Moreover, each copy of Explosion created with Radiate will use the same value for X as the original (C.R. 706.10).
Note that this answer doesn't depend on whether the Commander variant is played; in any case, nothing in the rules for that variant (under C.R. 903) explicitly precludes applying those rules to two-player games (C.R. 903.2).
EDIT (Oct. 10): Cite a more pertinent rule than C.R. 706.10e. Some other rules were renumbered with Core Set 2020. Correctness edit.
Peteroupc has the perfect answer, but I think it should be pointed out that in your question you asked about eliminating your opponents. If you radiate explosion, a copy will also be made targeting you! Have a plan in mind.
Moreover, each copy of Explosion created with Radiate will use the same value for X as the original (C.R. 706.10).
Note that this answer doesn't depend on whether the Commander variant is played; in any case, nothing in the rules for that variant (under C.R. 903) explicitly precludes applying those rules to two-player games (C.R. 903.2).
EDIT (Oct. 10): Cite a more pertinent rule than C.R. 706.10e. Some other rules were renumbered with Core Set 2020. Correctness edit.
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