Resistance target being basically the same (generally adding 2 stats together).
Delayed spells costing MP that can't be recovered until the enchantment ends.
(From Donjon) spend a round gathering magical energy before casting a spell. Casting from your personal reserves is very draining. The difficulty of that "gather energy" check is based upon how much mana is in the area. Priests get it easier if their deity is paying attention (such as in a temple). Otherwise, you need to contact them, first.
Gathering mana is generally quite obvious. The energies spark through the air as they are drawn into your body. You tend to acquire a noticable glow (a bit like the godlike halo) and the restrained energies crackle across your frame. This is a bit dangerous so it's good to dispose of that energy immediately. Casting botches (or being injured while holding that power) tend to cause you to take damage. Gods tend to just use internal mana, which doesn't share this vulnerability.
Internal mana comes back much more slowly... maybe something like it takes X days per point spent to get back 1 point. It's better to draw the energy from your environment, unless you're a deity, in which case you'll recover it comparatively rapidly (perhaps just 1 point per day, automatically?).
Your locale will determine the difficulty of the mana gathering roll. In a place with no magic, the difficulty may be incredibly high. In the presence of a god, you may get serious bonuses. I could even see saying that each successful spell casting bumps up the mana gathering difficulty by 1 point for awhile, at least in enclosed (mana-shielded) areas.