Reincarnation

In-game description:
"The Reincarnation process will reset all your stats, your excavations and remove all your gems. You will however keep your trophies and gain a new free upgrade, Reincarnation Power, unlocked immediately upon starting a new run. This upgrade will grant different bonuses based on the amount of times you have reincarnated and will persist through subsequent abdications. Certain reincarnations will also unlock new unique and powerful features."

Reincarnation was introduced in the Underworld Expansion (v1.2). In terms of game-play, it's a second kind of soft reset where players can trade in all of their gems and have most of their stats reset for other bonuses.

Requirement, Cost, and User Interface

Reincarnation can only be performed for the first time when the user reaches 1 Oc (1_E27) gems (not coins). Each subsequent reincarnation costs 1,000 times more gems.

When reincarnation becomes available, the "???" button on the Upgrades panel (to the right of the Abdication button) changes to a "Reincarnation" button.

Reincarnation Power

When you reincarnate the first time, you will automatically be awarded the Reincarnation Power upgrade. It is this upgrade that enables all the powerful reincarnation perks. Hovering over it will reveal all the details about your reincarnation perks.

Reincarnation Power Perks
In all formulas, x is the number of times reincarnated
R1	Increase production of all buildings by 25%Formula: $(25x)\%$* Increase offline production by 500%.Formula: $(500x)\%$ Increase Faction Coin find chance by 1%.Formula: $x\%$ Increase mana regeneration by 1.2 m/s.Formula: $floor(12.5 (\sqrt{(1 + 8 * x) - 1}) / 2) / 10$
R2	Increase production bonus from gems by an additional 0.2% per reincarnation. (starts at 0.4%)
R5	Increase assistants by 1 per reincarnation and increase the production of assistants by 2% per reincarnation made. (starts with 5 and 10%, respectively)
R10	Increase the production of all buildings over time based on the amount of times you reincarnated. Formula: $x^{(1.75)} t^{(0.65)}$ where t is the time (total) stat in hours*
R12	Increase maximum mana by 35 per reincarnation. (starts at 420)
R20	Increase the production of each building by 0.01% per reincarnation, per building of the same type. (e.g. 1000 Inns at R20 = 0.01% 20 * 1000 = 200%)*
R25	Increases Royal Exchange bonus by 0.5% per reincarnation. (starts at 12.5%)
R41	Increase the production of Unique Buildings based on the amount of times you reincarnated. Formula: $1200(x^{1.1})\%$*
R45	Increase maximum mana based on the amount of times you reincarnated. Formula: $70 x^{1.2}$*
R50	Multiplicatively increase Faction Coin find chance based on the amount of times you reincarnated.
R60	Increase Faction Coins found that match your Faction or Bloodline. Formula: $1.2x^{1.0}$*
R70	Gain one additional Research Slot in each branch.
R85	Gain 4 additional Assistants per reincarnation.
R100	Increase mana regeneration by 1% per reincarnation.
R108	Increase the production of Unique Buildings based on the difference of time spent as their respective faction against your most used faction in this reincarnation.
R115	Increase FC chance multiplicatively if they match your Faction or Bloodline or Artifact set (Stacks multiplicatively with R60 power) Formula: (1.2 * x ^ 1.05)

Reset and Kept Items at Reincarnations

Reset Items
Gems Locked Upgrades and Quests (Items that are visible but not unlocked) Found Faction coins and Royal Exchanges Excavations made Everything on the Stats tab, except the Times allied with at the bottom: Production stats Metagame stats Magic stats Faction coins stats of the Factions section

Kept Items
All Trophies (and trophy stats) Unlocked upgrades Heritages Excavation artifacts Rubies & Ruby Powers Completed Challenges Completed Quests (Faction, archeology, event, and research quests) Research unlocks (Slots, unlocked upgrades and RPs) Stats: Total times allied and spent in every faction. (Applies to Bloodlines, Faceless and research.) Feats

Progress Agenda (Goals)

Listed below are all the main progress systems and perks that you can get in Realm Grinder, excluding trophies, upgrades and Artifacts. The table also shows when, at which reincarnation level, which ones becomes available. All items require to be unlocked, except for the Spiritual Surge Spell, which is automatically granted upon reaching R14.

Reincarnation Unlocks
R#	Item	R#	Item
0	Heritages	27	Prestige Challenges (Tier 4)
0	Neutral Factions	29	Prestige Research
0	Prestige Factions: Dwarf & Drow	33	Prestige Challenges (Tier 5)
2	Vanilla Challenges (Tier 1)	40	Ascension ^[1]
3	Mercenary Faction	42	Tier Spell Upgrades
4	Neutral Challenges (Tier 1)	46	Neutral-Prestige Faction: Dragon
6	Prestige Challenges (Tier 1)	47	Dragon Research
7	Bloodlines	48	Dragon Challenge (Tier 1)
8	Vanilla Challenges (Tier 2)	51	Dragon Challenge (Tier 2)
9	Neutral Challenges (Tier 2)	54	Dragon Challenge (Tier 3)
11	Prestige Challenges (Tier 2)	57	Dragon Challenge (Tier 4)
14	Spiritual Surge Spell	60	Dragon Challenge (Tier 5), Lineages
16	Vanilla Research	63	Dragon Challenge (Tier 6)
18	Vanilla Challenges (Tier 3)	75	Mercenary Research
19	Neutral Challenges (Tier 3)	100	Second Ascension, New Alignments
21	Prestige Challenges (Tier 3)
23	Neutral Research
25	Neutral Challenges (Tier 4)

Also, try to get all the Faction Spell upgrades, Trophies and Artifacts you can along the way.

Guidelines

There are many paths you can take to progress, there is no "one correct path". Each player finds his/her own path, adapted to his/her play-style and personal progress. Trying to find your own path is the best way to learn and understand each faction.

The below is an example guideline but it is encourage to step out and try all the factions, note down which factions work best at which gem amounts and create your own progress path.

R0 - R16 Guidelines
R#	Range	Suggestion
R1-3	0 gems	Try Elf for at least the first run, for their high Faction Coin Find chance.
	~1 T (1_E12) gems	Try Titan, or Druid with enough excavations.
	~100 Qi (1_E20) gems	Try Fairy into Dwarf (Dwairies). Angel / Dwarf (Dwangels) also work well for those wishing to cast lots of spells fast and stack bonuses from them.
R3-12	1 No (1_E30) gems	Play as the above, and once you have reached 1 No (1_E30) gems, you are ready to try the Mercenary Faction. See Merc Builds and Magmardooom's guide.
R13-15	1 Vg (1_E63) gems	At this point, progress using Mercenary builds will start to slow down. The fastest choice is still Lightning Forge, requiring constant activity. A bit slower, but can almost entirely be idled, are the Innkeeper and Diamond Forge builds. Even longer, but solid, is the IGOT build which can go from 1 Uvg (1_E66) to 1 Tvg (1_E72) in one run. Optimize your runs by doing build-ups using special builds. (eg: Run "Foreplay" or "Everything is Awesome" merc builds to optimize your click total or your Faceless Heritage.) Once you reach R14 and have 6k+ mana, you can start to include Spiritual Surge in your combo casts. Note that there is not much benefit in solo-casting it or using it below 6k mana. If progress is really painfully slow, it may be time to consider getting those more challenging trophy and challenge perks you had put off until now.
R16+	1 Tvg (1_E72) gems	At minimum 1 Tvg (1_E72) gems, you may finally start Research! Out of all of the factions, Elf is well recommended for gaining Research points thanks to their Faction Coin generation. See also Research Builds.

Guides at Kongregate:

Guide R0 to R16 Optimized Gem Grinding by Magmardooom (Feb 11, 2016)
Guide for R0 - Starting Realm Grinder : R1 to R6 quickly, plus notes for everything before research by why_amihere (Oct 6 2015)
why_amihere's RG Speed Run Diary of a self-challenge: complete R0-R18 with all Challenges in 24hrs.

Related Trophies

Reincarnations Trophies
Name		Unlock Requirement
	1 Reincarnation	Reincarnate 1 time
	3 Reincarnations	Reincarnate 3 times
	5 Reincarnations	Reincarnate 5 times
	7 Reincarnations	Reincarnate 7 times
	10 Reincarnations	Reincarnate 10 times
	12 Reincarnations	Reincarnate 12 times
	15 Reincarnations	Reincarnate 15 times
	20 Reincarnations	Reincarnate 20 times
	25 Reincarnations	Reincarnate 25 times
	30 Reincarnations	Reincarnate 30 times
	35 Reincarnations	Reincarnate 35 times
	40 Reincarnations (PA)	Ascend 1 time
	45 Reincarnations (PA)	Reincarnate 45 times
	50 Reincarnations (PA)	Reincarnate 50 times
	60 Reincarnations (PA)	Reincarnate 60 times
	70 Reincarnations (PA)	Reincarnate 70 times
	85 Reincarnations (PA)	Reincarnate 85 times
	100 Reincarnations (PA2)	Reincarnate 100 times

References:

↑ Approaching R40, quantities in the game may behave strangely if any of the used values exceed the number 179.7 Uc (1.797_E308) because the computer can no longer store their values. This may not break your game in a noticeable way, but in general, values that overflow will get set to 0. If this happens, it will not prevent you from ascending, as gems cannot overflow before the gold does, but an overflow of gold will prevent you from any further gem gain.

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[1] Approaching R40, quantities in the game may behave strangely if any of the used values exceed the number 179.7 Uc (1.797_E308) because the computer can no longer store their values. This may not break your game in a noticeable way, but in general, values that overflow will get set to 0. If this happens, it will not prevent you from ascending, as gems cannot overflow before the gold does, but an overflow of gold will prevent you from any further gem gain.

[1]