MP means Magician's Pouch. If you have it, then you have access to several skills (including Red, White, and Black gem skills) that you would not have if you had not spent the 5 bucks.
I'd suggest taking all points out of Beam, Curse, Barrage, Slow, Armor Tearing, Ignition, and Demolition. Also, pick one : Bloodbound or Poolbound, and put the other's points into the one you selected. You don't need both, but at this point I'd suggest just using Poolbound (since it is much stronger at lower gem grades than Bloodbound is). Save some of those points for initial mana, but also put some of those skill points into critical hit and amplifiers (and traps, if you use those).
For your killing gem, use 1 grade 1 red, 5 grade 1 yellow, and 10 grade 1 white gems. Just combine them all together for a grade 4 gem. Use U to upgrade the thing, and use pure yellow gems in the amps. If that costs too much mana, then use 1 red, 2 yellow, and 5 whites. Try to keep the amps somewhat close in grade to the killing gem.
If you are attempting to set up a mana farm, use the same gem construction and amp construction, but use orange instead of yellow.
There are a couple things to note here. One is that you never want to use both white and black in a gem. They do not affect each other, only the rest of the specials and damage, and they are effectively added together to find the total power of the gem. At lower grades, any black you put into the gem would have been stronger as white. At higher grades (30+) any white you put into the gem would have been stronger as black.
Another thing to note here is that poolbound special, and bloodbound special, are not boosted by amplifiers. So, any use of white or black in an amplifier gem only reduces the total amount of power the amplifier provides to the tower/trap gem, compared to a similarly constructed gem without that black/white.
The last thing to note is gem usefulness. Combined with a grade 1 red and a grade 2 white, a grade 1 blue is going to be enough to significantly slow down monsters passing over that trap, just from the poolbound. Monster armor subtracts from the total damage done, per hit - after the damage has been multiplied by the critical damage multiplier, making yellow an incredibly strong damaging color, especially when boosted by black's or white's special. A critical hit gem, especially when you have the thing strong enough that you are at 80% chance of a critical hit, is going to be leaps and bounds more powerful than an armor tearing gem, and will be able to do damage to high armor monsters both must more easily and much sooner. The Bolt spell, when applied to a trap gem, makes that gem ignore monster armor in any case - whether the monster has 1 point of armor or so much armor that it is displayed in scientific notation.
