@pvtpyle Please share the following additional information that I think would be good to add to this guide. It is essentially a guide on the level up offers.
I don't know what level you are at, but at some point, you are going to wonder whether these level up offers are any good. I spent plenty of time missing out on great deals, because I did not know that they were predefined and there was some place I could look them up.
Review this web page before you play the game for long:
What follows is a general strategy that I would have followed had I known about this page. There are numerous times when a legendary comes up for 195 gems. It doesn't get any cheaper. Still you will need to decide if you want that particular monster. I would suggest that the ONLY must have (even with the advent of his archnemesis Faraday) is Voltaik at 54th level.
Note also that sometimes a pretty good offer happen back to back. A F2P player may need to prioritize which offers they go after.
Also another classic mistake that I see MANY players make is that they race through the adventure map and end up with an incredibly high level, but really low monster power. I think that is actually counterproductive, since it affects your ability to do well in certain challenges.
These suggestions ignore ALL of the offers that cost money, because this is for F2P players. I would also ignore all of the offers that combine legendaries with items or runes, because I don't think they are worth buying. You can craft runes up, although it is slow, but hey you are F2P, so you need to embrace that or start spending money. That is also why you need to watch the video on risk based run crafting.
I would NOT suggest doing any of the monster offers for gems that are NOT legendary, like Trevor at level 14 for 85 gems. While he is not easy to get, he is not worth the gems.
On the other hand, the following two offers are something a F2P player should consider since they cost gold, which they will have if they are willing to save.
13-LaCroc for 200k, why because you can't buy him for gold.
16-Phoenix Plume, Time Stop, Hex, amd Triple Strike for 200k, these are gems items otherwise.
Now here are some interesting points, where I would suggest that they try to get you to waste your gems.
53-Shi Hou+stuff: Don't do it, unless you can also afford Voltaik next level.
54-Voltaik: legendary for 195 gems. It doesn't get any cheaper.
If you don't have a lot of gems and waste them getting Shi Hou, then you will miss out on Voltaik. The same thing happens below for Cavenfish.
63-Firestorm: legendary for 195 gems. It doesn't get any cheaper.
64-Cavenfish: legendary+stuff for 225 gems. It doesn't get any cheaper.
In addition, Timerion cells show up at 67: 120 Timerion cells. A monster on sale is usually around 249 gems and with this, you will have 20 leftover.
The X Speed rune at level 76 for 500 gems is cheap, but if your Rune Building is not maxed there is no point in buying it.
Meme-master in his own mind.