Here is an excel spreadsheet that is fully filterable and sortable. You can organize by monster number (from the Monstagram), monster name, rarity, elemental types, books, relics, and stats (power, life, and speed). I've also added the trait or immunity each monster has. You'll need a recent version of Excel to run the macros properly (and may need to Enable Editing and then Enable Macros when you first load up the spreadsheet). If you find they don't work, just download the imageless version (at the bottom of this post) and use advanced filtering (described below).
HOW TO USE THE SPREADSHEET
To filter, simply click the image of the rarity, element, book, or relic you want to see. To clear a filter, just click the corresponding button to clear that particular filter. To clear all filters, just click the clear all filters button on the far right (you may get an error message if the filters are already cleared). The filters are additive: you'll see monsters that have ALL the items you've selected, click as many as you want! Only rarity and relic filters allow you select one at the time. If you notice all the extra columns on the right, leave them alone: that's where the magic is.
For advanced filtering, click the arrow at the top column to filter, move down to Text Filters, then select "Contains..." This will open a pop up window where you can type the word you want shown (e.g.- fire, female, trap, etc.). It's not case sensitive. If you want to do a little more advance filtering (like filtering all water/thunder monsters), in that box that popped up, click the radio button for "And", hit the drop-down box right below it, click "contains" and type the second term you're looking for. If you want, for example, to see all monsters in Dragons and all monsters in Underworld (not just those in both), click that "Or" radio button. If you need any help navigating the filters, feel free to post on here and let me know.
For the skills, I only pulled from skill groups 2 and 3, since skill group 1 is pointless 99% of the time (I know there are rare exceptions, so feel free to shout out any you think might need to be included). If an effect has only 50% chance of hitting, I haven't included it. I only included stamina drain skills that sap 50% or more of an enemy's stamina (so, I haven't included Stamina Leak or an attack that drains 25% stamina, for example). This should help you in narrowing down where to put your speed runes. At the present time, skills data is only available for legendaries.
On each sheet, there is a column labelled "Select". Use this column to compare particular monsters with each other. Or use it to keep track of monsters you own. If you type in an 'x' (without the quotes), the star icon at the top will automatically filter this column.
The second tab at the bottom is a damage calculator. The highest powered attacks for legendaries should help you decide where to focus your strength runes.
Only legendaries are in this list, as you're not likely using another rarity to attack with. One of the many factors in damage calculation is your monster's level compared to the defending monster's level. As my stats are intended to help you decide which monster to choose (compared to other monsters) this formula assumes both you and the defender are level 100. The sheet already has the monster's base power and highest attack value filled it. If you want to know the damage output of any skill, just plug in that damage value of that skill instead.
There are other damage modifiers there as well after you get the base damage. Element Damage refers to a regular attack (1), strong (1.5) or weak (0.5) attack, or some other kind of elemental weakness like sticky lava, light weakness, etc. (1.8). The options there are fixed so just select the one that applies. Attack modifiers are for things like damage boost (1.5), double damage (2), or triple damage (3). Again, the numbers there are fixed and, if normal damage, just leave 1. For runes, add up your total strength rune bonuses and convert it to a decimal (move the decimal point over two places). The formula will take care of the rest.
Don't just view it in your browser (it'll look awful and won't be interactive). Be sure to download it.
If you see anything needing fixing, let me know! The link in this post will always have the latest version. Hope this helps everyone!