For example, if you were casting Serra Angel, which costs, you could tap three basic lands of any type to pay plus two Plains to pay
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Wind Crystal's first ability)
If you really want to make Trepanation Blade work, try to weave exile into the deck
The Vault is surprisingly good in cube, it is usually comparable life to Vampiric to find a specific thing yet it also has the capacity to tutor for a couple of more vague things, say two lands and any sort of three drop
3) Enel (Yellow) The reigning king of the Life Trigger lottery, Enel has a very safe Leader ability (that lets him heal when he drops to zero life) and access to a whole pile of generically strong Yellow Characters