I don't consider myself a good builder... I try to put some thought into what I do and then spend forever tweaking
Well this is sorta a transformational sideboard. Of course I'm not gonna describe what exact numer I'd bring in vs each single build, but I can give the general gist of the thought process.
vs aggro/tempo/tribal I'd go this way :
+1 Bounding Krasis +2 Reclamation Sage + 1 Drowner of Hope+1 Eldrazi Skyspawner +1 Adverse Conditions +3 Jadi offshoot +1 Woodland Bellower
-3 Mwonvuli Acid Moss -1 Ulamog -1 Oblivion Sower -1 Part the Waterveil -1 Disciple of the Ring -1 Nissa's Renewal -1 From Beyond -1 Greenwarden of Murasa
This way it becomes a token themed midrange deck with boardwhipes and some lifegain. Should be pretty though to burst through. Gain some life, Ramp some, make em spend burn on your dorks.
Wave/whipe the board. Drop walkers and bodies and beat face. Emblemed Skyspawners / Drowners/ Bellower are .... obscene.
VS draw- go control :
+1 Bounding Krasis +1 Reclamation sage +1 Woodland Bellower (enchant tech and more bodies) +2 Gaea's revenge (duh) +1 Eldrazi Skyspanwer (good for faster stronger plays and good vs walkers)
-1 Adverse Conditions -1 Drowner of Hope -1 Displacement Wave -2 Planar Outburst -1 Part the Waterveil
VS ramp :
+2 Angelic Edict +1 Suppression Bonds +1 Skyspawner
-1 Adverse Conditions -1 Drowner of Hope -1 Gideon (firecraft, rolling thunder, tramplers... meh) -1 Evolutionary Leap
Basically I wanna win this by ramping faster than him, get the first moss in; then kill him with a Displacement wave(which is sometimes like
upheaval in an artifact deck from 15 years ago
brooooken)/Greenwarden/Lumbering Falls combo or by 'tricking' his ulamog by playing mine first, then dispersing my ulamog as he casts his to target mine.
Since ramp vs ramp is 90% of the time about getting the first Moss in, and I run no counterspells, being on the play is stupidly important. The skyspawners help you cast Ulamog /go ham with comboes faster than your opponent. On the play this deck is heavily favourite vs other ramp because of this. On the draw, I'll take anything that ramps hard and has redundancy in the mana, and hope to snag his important plays with the white spot removal later.
Main weakness is Rolling thunder. We do have Disciple and the double Renewal to help with this though.