Caleb Drakesoul was a gestalt Druid/Wizard using every trick available from both 3.5e and PF1e to let him play around with ley lines or the like. I was able to use the combo combo of an obscure feat plus the normally-trash Geomancer prestige class to have all of his Druid spells work entirely off Intelligence. Specifically, the feat is Academic Priest from the oft-forgotten "Legends of the Twins" Dragonlance book; Academic lets a character use Intelligence for maximum spell level and bonus spells per day, rather than Wisdom (and the equivalent "Dynamic Priest" lets you use Cha instead), but explicitly has no effect on save DC. Geomancer, on the other hand, allows you to use spells up to your Ley Lines limit (0th/1st/2nd/etc. up to 9th level at Geo 10) with whatever combination of casting attributes you prefer, and specifically your arcane spellcasting stat for all DCs, but doesn't affect max spell level nor bonus spells per day. So, by like Geo 5 or 6-ish, which is where that campaign originally started, he was a SAD Druid/Wizard. His whole thing was unraveling the true nature of the cosmos.
I also managed to squeeze in Dragon Wildshape so he could turn into a dragon, frankly less powerful than most of what he could do but a lot of fun for me. Got approval from the GM for some slight tweaks to the Geomancer "drifts" so that, even in his "natural" form, Caleb functionally looked like a dragonborn despite being mechanically half-elf IIRC.
My spells were split about 1/3 each between self/group buffs, healing/summoning, and damage/utility, but really the single most powerful thing I could do was from Pathfinder's "Void" elemental spell school. That school power is nuts: no-save, (3+Int mod) uses-per-day, one-round (CL/2) penalty to ALL saving throws and AC(!!) for a chosen target within 30 feet. With my items, Archmage powers, Menhir Druid stuff, Void stuff, feats, etc., that meant something like a -14 to all of an enemy's defenses, and I had enough Int to use this almost freely. Sure, that would eat my standard action, but with that much penalty it functionally meant guaranteed fails on saving throws and guaranteed hits for my melee-attacker allies, so any singular big nasty was rarely much of a threat.
But most of the time my spells were going toward healing (as the party needed a healer), buffing, summoning, or solving non-combat problems. Another great spell I made extensive use of was rain of roses, as it is both entirely nonlethal and does no harm to non-evil creatures. (All evil creatures take temporary wisdom damage while in the area of effect and fall unconscious if they are reduced to 0 Wisdom, and separately there's a Fort save or the evil creature is Sickened while inside the 80' radius cylinder.)
I'll add, since this was mostly asking WHY we like certain things, I did this in part because I wanted to have a character that could really make Geomancer awesome. Because in concept it's really cool! Someone taking in the essence of the land in order to get at the fundamentals behind all magic, which changes them into something slightly beast-like; enlightenment which results in a more "bestial" appearance, not less. The problem is, Geomancer sucks in ordinary (non-gestalt) play. It's a PrC that requires dual casting to enter, but ONLY advances one "track" at a time. (That's why the GM approved taking both Geomancer and Planar Shepherd. Both PrCs only advance one spellcasting class, not two.) In a gestalt game, Geomancer can be really cool if you can use it effectively--it obviates Arcane Spell Failure, for instance, and allows things like Divine Metamagic to apply to Arcane spells (since you can freely mix-and-match all spellcasting characteristics except bonus spells and max spell level, up to a spell level of Geomancer level minus one.)
I then just...collected bits and pieces that fit together to make an intellectual, planar-cosmologist druid-wizard. Very very much "Selesnya" with a big side helping of Blue, for folks familiar with MTG color concepts. (Basically, growth, tradition, and the natural order allied to morality, "the good of the many", and order/peace, but with an eye toward progress, perfection, and knowledge.)
