Alternating patterns of small and large amplitude oscillations occur in a wide variety of physical, chemical, biological and engineering systems. These mixed-mode oscillations (MMOs) are often found in systems with multiple time scales. Previous differential equation modeling and analysis of MMOs has mainly focused on local mechanisms to explain the small oscillations. Numerical continuation studies reported different MMO patterns based on parameter variation. This paper aims at improving the link between local analysis and numerical simulation. Our starting point is a numerical study of a singular return map for the Koper model which is a prototypical example for MMOs that also relates to local normal form theory. We demonstrate that many MMO patterns can be understood geometrically by approximating the singular maps with affine and quadratic maps. Motivated by our numerical analysis we use abstract affine and quadratic return map models in combination with two local normal forms that generate small oscillations. Using this decomposition approach we can reproduce many classical MMO patterns and effectively decouple bifurcation parameters for local and global parts of the flow. The overall strategy we employ provides an alternative technique for understanding MMOs.Keywords: Fast-slow system, Koper model, return map, mixed-mode oscillations, local-global decomposition.Complex oscillatory patterns have been observed in a wide variety of applications. Analyzing these patterns from a dynamical perspective has been an active area of research for decades. However, several mathematical breakthroughs in the last 15 years have provided substantial additional insight into phenomena that describe local oscillations. In the present paper, we provide a numerical study of the singular Poincaré map in the Koper model. We demonstrate that many MMO patterns for the Koper model can already be understood just using approximations of singular limit maps. The results for the Koper model suggest that a local-global numerical simulation approach combining normal forms with discrete maps can be effective. We show that this abstract approach reproduces many typical MMO patterns that have been observed in applications. This methodology aims to close a gap between previous numerical studies of MMO patterns and analytical results about local normal forms.