Primal command if noncreature target is illegal does it fizzle

[Nidorino]

If I cast Primal command and non-creature target becomes illegal, does the spell fizzle?

[Arix]

It depends on what else you chose. A spell is countered if all of its targets are illegal. If you also chose the "gain 7 life" or "shuffle graveyard into library" mode and the target palyer is still legal, the spell will resolve and do as much as possible (cause the targeted player to do the selected action). If you chose the "search for a creature" mode, then since its only target is now illegal, the entire spell is countered.

[Kenji]

A spell only "fizzles" (not an official game term; "is countered upon resolution" is more correct) when all of its targets are illegal as it attempts to resolve. Here's some text from the Comprehensive Rules:

608.2b If the spell or ability specifies targets, it checks whether the targets are still legal. A target
that’s no longer in the zone it was in when it was targeted is illegal. Other changes to the game
state may cause a target to no longer be legal; for example, its characteristics may have changed
or an effect may have changed the text of the spell. If the source of an ability has left the zone it
was in, its last known information is used during this process. The spell or ability is countered if
all its targets, for every instance of the word “target,” are now illegal. If the spell or ability is not
countered, it will resolve normally. However, if any of its targets are illegal, the part of the spell
or ability’s effect for which it is an illegal target can’t perform any actions on that target or
make that target perform any actions. The effect may still determine information about illegal
targets, though, and other parts of the effect for which those targets are not illegal may still
affect them.

Bold and underline emphasis mine. So, your answer depends on which other mode you selected for Primal Command. The other three are these:

- Target player gains 7 life.
- Target player shuffles his or her graveyard into his or her library.
- Search your library for a creature card, reveal it, put it into your hand, then shuffle your library.

If the other mode selected was either of the "target player" effects, then you'll still get that to happen on resolution. However, if you chose the library search as your other mode, Primal Command is countered because all of its targets have become illegal.