Delayed Spellcasting (3.5e Variant Rule)

Delayed Spellcasting
This spellcasting nerf technically extends spellcasting time by delaying when in initiative the spell goes off.

When casting a spell, the spell does not go off right away, but instead goes off as if your initiative was your initiative result - the spell level. What this means is that a wizard could cast a spell, then have the fighter's turn occur before his spell completes (leaving him open to be attacked in the middle of casting). The only guarantee is that the spell is completed before the beginning of his next turn. This method is a bit more complicated, as initiative order must be tracked, but weakens spellcasting without actually increasing casting time itself and consuming move actions or other actions.

If the delay pushes the spell's casting past the lowest initiative -1, it goes to the top of the initiative and goes down. No matter how large the delay from spell level, the spell always goes off at least before the caster's initiative +1.

Example
The wizard gets an initiative of 15, placing him in the following order: Rogue 25, Wizard 15, Goblins 10, Dragon 8, Fighter 2. The rogue goes normally, and the wizard casts fireball, a level 3 spell. The spell is a standard action and goes off at initiative 12 (15 - 3 = 12), before the goblins as normal.

The next round he casts horrid wilting, a level 8 spell. The spell goes off at initiative 7. The goblins and dragon take their turns before the wizard can finish casting, either moving out of the way of the spell, disrupting the spell, or other actions.

In another combat the wizard rolls a different initiative: Rogue 22, Bugbear 16, Fighter 11, Wizard 2, Troll -1. He casts horrid wilting again, putting him 3 points down (-3) before looping around and counting from 22, the highest initiative, 5 more points. The spell's initiative is now 17, which goes before the bugbear just barely. Then, he manages to get a hold of some crazy 99th level spell that doesn't exist but does for the purpose of the example. The initiative penalty is -99, but it'll go off before his initiative (initiative count 3 in this case) anyway.