Cards are exclusively from the 4 following blocks :

• MMQ
• INV
• ODY
• ONS

This is in my opinion one of the sweetest spots in mtg history, set between 2 of the most broken sets ever printed (Urza & Mirrodin).

Some of the mechanics introduced in those sets are amongst the best ever designed : kicker, cycling, flashback...

So this cube doesn't intend to emulate any particular format, but act as a kind of recap for that time period.