How can you guys go through spikes? I don't understand it's worst than pirhana plants in SMB1

For landing on top of spikes, you have to land on the ground with a tiny upwards speed. For example, if you land on a spike with an speed of 0.1 px/frame upwards, you have 10 frames to run along the spikes before the game pushes you up a pixel and you start to fall onto the spikes.

For wall-jumping off of spikes, you can only do it off of left-facing spikes, and you need to somehow make your x-coordinate an odd number. The easiest way to do this is to move the character against a wall or the boundary of the game. Having an odd x-coordinate makes the hitboxes just line up in a way that lets you get close enough to the wall behind the spikes to wall-jump without hitting the spike.

For dashing through spikes (can only be done in 2500m), you need spikes that don't have a wall behind them. If you get close enough to the spikes and dash in their direction, it's possible to completely hop over their hitbox (again, if there's no wall behind them to bump into).