The Frost Weaver is an ice spirit that is one step evolved from the base of the spirit species. Its growths are moderate and flat across the board, but if one were evolved from the base spirit, the Frost Weaver has an easy access to rather impactful frost skills.
While the Frost Weaver is not an Elite, it has no further evolution and loses the Evolving special trait.
The Frost Weaver is the arachnid form that is found in many spirit elements, bringing the utility of Net to the player's team. Where the Frost Weaver differs is that its default attack is Ranged Frost damage and it has convenient access to terraforming skills.
Being a non-Elite spirit with no evolution, one may not think it necessary to raise a good Frost Weaver. This is, to some extent, true - unless the player is going for a team composed solely of ice spirits, there are many options that serve better than a Frost Weaver in many situations. The spider's Jumping movement and Ranged Frost damage can be critical, however, especially if the team uses Frost damage in the first place. This spirit can easily move into the thick of battle and apply a dose of Chilled on an already-Chilled enemy, upgrading the debuff to Frozen. Of course, the Frost Weaver also probably has access to Freeze, so it can Freeze another enemy while there as well.
Another thing to note is the Frost Weaver's easy access to Snow, a map-wide terraforming skill, and FrostNova. Snow does not create as many snow tiles compared to other map-wide terraforming skills, but this option is still the easiest access to a terraforming skill ice spirits get. Frost Nova also has a terraforming component, but what's more important is that it inflicts area-of-effect damage and Frozen debuff over two hexes centered on the user. Having a Frost Weaver jump into the middle of an enemy position on the first turn and cast Frost Nova can Freeze most of the enemy team before the battle begins. Sadly the Frost Weaver gets no real benefit when it comes to actual enduring damage, so retrieving the spirit may become a complicated maneuver.
Overall, the Frost Weaver is the generalist of the ice spirits' arsenal. It's not impossible to raise one as a formidable combatant but it may be more useful to think of the Frost Weaver as a source of rare, powerful skills.