@Karsten75: You'll need constantly upgraded manafarms and plenty summons to achieve G20+ gems. And I guess you'll need at least wizard level 100 with specific skills... Learning is a time consuming procedure :-)
As you can see on the previous pages, Grade 100 Gems are possible
My highest grade gem WITHOUT exploiting a glitch was a G27 gem, but then I got bored. I could have gone much highter (into the 40s...) but you don't need that.
Just use mana farming, then it is easy to get Grade 20+ gems.
Appendix to Michan666: - to beat 3,333m hp cap monsters you will need a ~G22 Y/L - to beat 9,999,999m hp cap monsters (the new update's higher setting), you will need a ~G30 Y/L
Upgrade your trap skill to max and put high grade orange/lime gems into the traps at the places where the monsters enter. Start with a grade 5 one, or two, and slowly updrade them, take your time.
spend most of your mana on that, at the start. Only start building your damage gem once you got a good manafarm going.
It might be helpful to know whether you have premium or not. With premium it might be easier, and what wizard level are you? I am wizardlevel 480...
Those will leak so much mana that you can easily duplicate grade 18 gems, soon, and combine them till you get a grade 27 gem.
I have premium level (was happy to give Peter my $5) and I'm lvl 62 wizard. I'm having a really hard time finding a way to get a good breakthrough into higher Wizard levels.
Mostly we talk about wiz level well over 100 these days for some reason Even non-premium, you can squeeze 30 levels out of the first and second pylon maps easily enough and that's enough to start doing the advanced cheese (I did that on first pylon map around wiz level 20). I posted a strategy for that in the linked thread. Oh, and that's enough to max wild gem skill which is enough to throw in a tower and forget to do many maps until the end.
After that, it's just getting your feet until you can kill max hp creeps (endurance). Replenish skill = more mana per creep killed, so that you can summon more creeps and will be gaining mana (and use this mana to set up a mana farm). Granted that's not needed with the currently broken auto-extend feature, but don't depend on that forever
I finally completed my first max multiplier 1337 run (missed 4 battle amulets. How do you get kills with shrines? they don do hardly any damage? Also its impossible not to have any monsters get to your orb)
I got my multiplier up o 420, but that was by 0.05 incriments and it took me like 1000 waves. how do you guys get so much mana pool?
I was able to get a big gem, but it took forever and the game basically freezes when I duplicate, I dont know how to get higher level gems, this one took me the whole game to get
Also, the new patch raised the monsters max health by a LOT
I angered the crap out of the final wave, just because I can
I didnt get any kills with my shrines. How do you guys kill stuff with shrines? do you do it at the start? Shrines seem to be good for cutting down monster HP, but they cant kill anything