Solitary Cell

Two mana to exile a nonland permanent up to mana value 3 is efficient interaction for Mardu; the legendary discard ability is only minor filtering.

Could be wrong if A hostile artifact-removal environment or mana pressure could make a two-color sorcery-speed answer worse than existing removal.

It covers mana value 3 where Portable Hole stops at 2, but the extra mana and red requirement make it less splashable and less tempo-efficient.

Could be wrong if Portable Hole and cheaper colored removal may remain preferable, leaving this as only a narrow metagame option.

Boros Energy can use an artifact answer to cheap permanents, but two mana, two colors, and vulnerability to artifact removal are meaningful Modern costs.

Could be wrong if If the format's key threats sit at mana value 3 or less, its broad target range could support more maindeck adoption.

It can answer many cheap permanents, but Legacy strongly punishes a two-mana, two-color, sorcery-speed removal spell that can be undone by artifact removal.

Could be wrong if A specific cheap-permanent metagame or artifact-prison shell could make its mana-value-3 coverage more valuable than expected.

Cheap exile for mana value 3 or less is useful but narrow in multiplayer; legendary cards can turn the activation into repeatable filtering, not card advantage.

Could be wrong if Its ability to answer commanders is reduced by the command-zone replacement option, and artifact removal can restore the exiled card.

A two-mana exile effect for most early creatures and many noncreature permanents is premium removal, though it misses expensive bombs and needs both colors.

Could be wrong if Unknown set speed, fixing, and creature curves may make the mana-value restriction or gold cost substantially more punishing.