It looks like there may be a bit of confusion in your question, as "keystone" is typically used in ecological contexts to describe a species that plays a critical role in maintaining the structure of an ecosystem. Each of the terms you've mentioned—mouse, frog, deer, and "frasshopper" (which seems to be a typo for "grasshopper")—represents different types of organisms.
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Keystone Species: This refers to a species that has a disproportionately large effect on its environment relative to its abundance. For example, sea otters are considered a keystone species because they help maintain kelp forest ecosystems by controlling sea urchin populations.
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Mouse: Mice are small rodents that can serve as prey for a variety of predators, playing a significant role in the food web.
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Frog: Frogs can also be considered keystone species in some ecosystems, especially in wetland habitats where they help control insect populations and serve as both predators and prey.
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Deer: Deer can influence their environments significantly through herbivory, affecting plant community composition and structure. In some ecosystems, they might be considered keystone species due to their role in shaping the vegetation.
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Grasshopper: Grasshoppers are herbivorous insects that can impact the vegetation in their habitats. Their feeding habits can influence plant community structures and also serve as a food source for many animals.
If you're looking for specific information about the ecological roles of these animals or a particular aspect of one of them, please clarify!