Regular Powers are powers that can be obtained only through power rolling through the in-game shop, then clicking "Powers". Power Rolls are used in this page to roll for regular powers and each power has their own rarity. You may obtain power rolls through events (such as Admin Abuse), quests, winning in a non-hardcore round (awards 1 power roll), winning in hardcore (2 power rolls) or AFK World. There may be other ways to obtain power rolls such as the monkeybars mini-game on Dalgona.
This page also has a Pity system that awards a free Mythic rarity (not a duplicate, unless if all mythic regular powers are owned already) which requires 199 rolls by the weekend, or 225 during the weekday. The maximum pity requirement will be (apparently) changed every 12 AM EST on the weekend/weekday where applicable.
Once Pity is reached, it will be locked until manually unlocked by developers (which always usually happens every update). If you roll a Mythic power but not from Pity, your current Pity will be RESET instead of locked. You cannot roll duplicate Mythic powers from Pity, although rolling a duplicate Mythic without Pity does still reset it. Pity can only be increased from using Power Rolls, or Guard Power Rolls.
Purchasing Power Rolls has the same price as per buying Guard Power Rolls, which buying one costs 175 Robux (~2.17 USD) and buying 10 as a bundle in-game for 1,669 Robux (~20.65 USD). Purchasing 10 (Guard) Power Rolls as a bundle instead of buying 10 individually saves 81 Robux ... it's not recommended to buy rolls as they are overpriced and can be obtained easily by simply playing.