I've been playing Tap Titans 2 on my iPhone 7 the past few days and have really been enjoying it. Those who know me, know that I was HEAVILY addicted to MMORPG for a long time and this game has really helped fill the void left when I sold my desktop. The idea of the game is to tap your screen, until titans die, then tap more.
This game has great character build/skill tree options, and can be played at leasure. It also helps that the main character is blatantly designed after Cloud Strife from Final Fantasy VII.
Each stage consists of 10 Titans, 9 of which are peons, the 10th being a mini boss. Every 5 levels you fight a real boss to change the scenery and earn bonus gold.
Your character is leveled up using this gold and your strength becomes multiplied x2 or x3 every 20 levels. DPS increases slightly each individual level.
You hire heroes with gold as well, to help beat titans faster, and also earn more gold while the game isn't active. These heroes can be leveled up and strengthened (to the point they are stronger than your main hero.)
Pets are obtained from eggs (given every 3 hours.) These increase in strength as your main character does. They can enhance your hero damage, pet damage, tap damage, all damage, and/or gold. The multiplier increases as the pet increases in it's own level.
Every 100 levels (up to 600) you have the option of purchasing a new skill as well. Fire sword and War Cry being the most efficient for damage, and Hand of Midas being the best for gold acquisition.
At level 600, you have the option of using Prestige, which starts you back at stage 1. The goal of using Prestige is to earn relics and skill points. Relics can be traded for artifacts, which are used to increase DPS, gold, etc. Skill Points are used to upgrade/obtain skills that increase pretty much every aspect of the game.
Diamonds are your P2W items that let you double damage, swipe to hit, buy upgrades, etc. (Don't be that person who drops $100 on diamonds.)