Ultrafast spin dynamics is one of the promises of antiferromagnetic spintronics, but the vanishing magnetization poses a great challenge to the detection of antiferromagnetic materials. Ferrimagnets (FIMs), on the other hand, can be operated as antiferromagnets with similarly high frequency while being able to be detected as ferromagnets. Therefore, exploring the physical behavior of FIM is essential to inform the research on antiferromagnets. In this talk, I demonstrate a series of static and dynamic properties of a two-sublattice FIM in response to a magnetic field and a current producing spin-transfer torques. By identifying the ratio of the two sublattice spins as a key variable, I show how the fingerprint features of antiferromagnets can change, evolve, and survive in FIMs, which includes the spin-flop transition, the sub-terahertz exchange mode, and the auto-oscillation induced by currents.