Explain the concept of "field spells" in Riftbound.

Field spells in Riftbound are designed to influence the battlefield’s characteristics significantly. These spells create an ongoing effect that can change various aspects of the game environment, such as giving bonuses to certain units, altering terrain, or providing unique advantages that players can utilize strategically throughout the match.

This characteristic of field spells allows players to implement long-term strategies that can affect the course of the game, rather than being limited to one-time use spells or effects. Understanding how field spells interact with other game elements can be a key component in mastering gameplay and leveraging one's strategy against opponents effectively.

The other options suggest that field spells either have a negative impact, such as enhancing opponents' units, are only applicable at certain times in the game (like match end), or are ineffective in influencing gameplay altogether. Such interpretations do not align with the fundamental mechanics of field spells, as their primary role is to actively shape the game environment in favor of the player using them.