The enemy can probably keep you from the grail after seeing you grab it the first time. So just fireball as many people as possible. Even with thornplants recognizing him, he can take out 2 plants. Now that 2.5 is out the ice wizard's lifespan is considerably smaller. Defending is harder as people get better and everyone kills ice wizards better.
Newbies ask which wizard is best.
The plant wizard is now the best wizard. Put your plants NEAR a resupply so you can build them up as fast as they go down. If you need to shoot someone far away, thornblast. If you need to shoot someone up close, thornblast. If you need to take out a lvl 1 plant, shoot it with MM or 1 once with thornblast as you advance, then once at point blank range.