Example repo on how to take a flash loan with DyDx from ( https://etherscan.io/address/0x1E0447b19BB6EcFdAe1e4AE1694b0C3659614e4e )

1. npm i

1. npm run flat
2. Copy content from the FlashloanTaker.flat.sol file to the Remix.
3. Remove the second pragma experimental ABIEncoderV2;
4. Deploy contact with tiny amount of token at the time of deployment

1. cp .env.example .env
2. Specify PRIVATE_KEY and GAS_PRICE in the .env file
3. npx truffle migrate --network mainnet --reset
4. Send a tiny amount of the token you want to borrow to the smart contract. E.g. if you borrow WETH the FlashloanTaker has to have 1 wei (one wrapped wei) on the balance.

1. aave

1. Refinancing. Refinance your interest to a lower interest in another lending protocol. Taking flash loan from Aave in Dai, closing a CDP by sending the Dai to the CDP, taking the ETH which was as a collateral to Compound (whichever has better interest rate for borrowers)
2. Closing CDP. The same as above but just closing the CDP without any DAI.
3. Arbitrage.