Tikki Tooki is the trickster serpent god. He has a particular soft spot for gold, accepting it as tribute and granting it to faithful followers. This makes him quite versatile both for purist runs (where gold is in short supply) and with heavy preparations (where you often have more than you can spend).
Tikki Tooki is uncovered in the south in a large subdungeon where you must play "tag" with an imp to prove your worth to the deity.
Tikki Tooki is very difficult to earn piety with as a low-level character, since he punishes you for taking too many hits, and gives piety only for killing lower-level monsters. Of course, low-level characters are unlikely to be able to win their fights with a single blow, and there are few monsters lower-level than they are (which they probably shouldn't be fighting this early, anyways). This makes him very distinctively a deity you worship later on, unless you can tribute large amounts of gold to keep him happy.
Generally speaking, the best approach to Tikki Tooki is to begin your worship with lots of popcorn monsters left in the dungeon. Purchase the Tikki's Edge boon to increase your piety gain from killing these low-level monsters, then complement with boons such as dodging or reflexes to gain his special potions. Another strategy is to begin worship early and use desecration or tribute to quickly purchase the "poison" boon, then convert to another religion to avoid the piety penalty for taking repeated hits. A poison attack is a very powerful benefit if you can obtain it early.
Tikki Tooki's potions are poorly described and poorly understood. The quicksilver potion causes your chance to dodge to increase for each consecutive attack you take, and becomes exhausted when you finally achieve a dodge. It also tells you when you're about to dodge, letting you predict which blow will be avoided. By attacking weaker monsters, you can keep taking minor attacks until your next blow will be a dodge, letting you avoid damage from a powerful enemy. The reflex potion grants you temporary first strike, and under some conditions may grant you two attacks. If you have a knockback attack, you will knock the enemy back twice when using a reflex potion, causing extra damage.
One little-known trick with Tikki Tooki is that plants can be farmed for piety. It's entirely possible to dodge a plant's "attack" against you, and Tikki Tooki rewards you with piety every time you dodge. This means a Tikki Tooki follower can build up large amounts of piety just by clearing plants (this is also possible with Jehora Jeheyu, but that deity doesn't offer a boon that enables you to dodge). As well, attacking plants will trigger the quicksilver potion, causing your dodge chance to rise. In this way, you can continue to attack plants until your next attack is predicted to be a dodge then attack the boss. On levels with large numbers of plants (Western Jungle, Southern Swamp, and Ick Swamp being the most common) this can make Tikki Tooki a very powerful deity, and also an exceptional choice to convert into after worshipping the Earthmother.
Overall, Tikki Tooki is one of the best "last hour" deities, offering enormous amounts of piety for slaughtering defenseless monsters and superb boons which can improve your odds.