Deadmau5 is one of the biggest names in Electro and Progressive House. What makes those genres is the idea of making Bass audible compared to earlier House genres. In Electro House this was achieved by layering higher Synths, mostly an interval of 3,4,5,7,or 9 Semitones with Sqare or Saw Waves. In Progressive house this was achieved by using Plucks that play Chords + Bassline + Leadline. Those plucks were made by Sawaves with a LP Filter Envelope.
In Hey Baby it sounds like a typical Electro Saw Bass. It is achieved by playing Saw waves in a low register. Over the time producer used several techniques to get a bigger clearer and fatter Saw bass.
Usually the sound is bade by 2 Sounds. One Sub bass synth (Deadmaus likes to use a minimoog here) that simply plays a Saw bass in a low octave. Sometimes it makes sense to filter this layer with a lowpass, depending on the layer you put above.
Ontop of this you want to layer the dirty,fat, distorted layer. To get this you can try the following things saw waves + a bit of noise slightly low passed. Then eq out the bottom end and boost by huge amounts at around 200-400 hz and a huge amount between 1000-3000hz then use distortion. Then add some modulation fx like chorus phase flanger and some reverb. Finish off with limiting the sound.
Deadmau5 uses a lot of analogue stuff like moog and virus. So he has a very warm sound to start up.